Natural history: general and particular, by the Count de Buffon, translated into English. Illustrated with above 260 copper-plates, and occasional notes and observations by the translator. [pt.2]

GENERAL HISTORY OF ANIMALS.

CHAPTER I.

Analogies between Animals and Vegetables.

AMONG the numberless objects with which the surface of this globe is covered and peopled, animals deservedly hold the first rank, both on account of the relation they stand in to man, and of their acknowledged superiority over vegetable and inanimated matter. The senses, the figure, and the motions of animals, bestow on them a more extensive connection with sur|rounding objects than is possessed by vegetables. The latter, however, from their expansion, their growth, and the variety of parts which compose them, are more intimately related to external objects than minerals or stones, which are per|fectly inert, and deprived of every vital or active

principle. It is this number of relations alone which renders the animal superior to the vege|table, and the vegetable to the mineral. Man, if we estimate him by his material part alone, is superior to the brute creation only from the number of peculiar relations he enjoys by means of his hand and of his tongue; and, though all the operations of the Omnipotent are in them|selves equally perfect, the animated being, ac|cording to our mode of perception, is the most compleat; and man is the most finished and perfect animal.

What a variety of springs, of powers, and of mechanical movements, are included in that small portion of matter of which the body of an animal is composed! What a number of rela|tions, what harmony, what correspondence a|mong the different parts! How many combina|tions, arrangements, causes, effects, and prin|ciples, all conspiring to accomplish the same de|sign! Of these, we know nothing but by their results, which are so difficult to comprehend, that they only cease to be miraculous from our habits of inattention and our want of reflection.

But, however admirable this work may ap|pear, the greatest miracle is not exhibited in the individual. It is in the successive renovation, and in the continued duration of the species, that Nature assumes an aspect altogether incon|ceivable and astonishing. This faculty of repro|duction* 1.1,

which is peculiar to animals and ve|getables; this species of unity which always subsists, and seems to be eternal; this generative power which is perpetually in action, must, with regard to us, continue to be a mystery so pro|found, that we shall probably never reach the bottom of it.

Even inanimated bodies, the stones or the dust under our feet, have some properties; their very existence presupposes a great number; and matter, the most imperfectly organized, possesses many relations with the other parts of the uni|verse. We will not assert, with some philo|sophers, that matter, under whatever form it appears, is conscious of its existence and of its relative powers. This question belongs to me|taphysics, of which we intend not here to treat. We shall only remark, that, being ignorant of the extent of our own connections with exter|nal objects, we cannot hesitate in pronouncing inanimated matter to be infinitely more ig|norant. Besides, our sensations having not the most distant resemblance to the causes which produce them, analogy obliges us to conclude, that dead matter is neither endowed with senti|ment, with sensation, nor with a consciousness of its own existence. To attribute any of these

faculties to it, therefore, would be ascribing to it the power of thinking, of acting, and of per|ceiving nearly in the same manner as we our|selves think, act, and perceive; which is equally repugnant to reason and to religion.

With inanimated matter, therefore, though formed of dust and clay, we have no other relations than what arise from the general pro|perties of bodies, namely, extension, impene|trability, gravity, &c. But, as relations purely material make no internal impression on us, and, as they exist entirely independent of us, they cannot be considered as any part of our being. Our existence, therefore, is an effect of organi|zation, of life, of the soul. Matter, in this view, is not a principal, but an accessory. It is a fo|reign covering, united to us in a manner un|known; and its presence is noxious. Thought is the constituent principle of our being, and is perhaps totally independent of matter.

We exist, then, without knowing how; and we think, without perceiving the reason of thought. But, whatever be the mode of our being, or of our thinking, whether our sensa|tions be real or apparent, their effects are not the less certain. The train of our ideas, though dif|ferent from the objects which occasion them, gives rise to genuine affections, and produces in us relations to external objects, which we may re|gard as real, because they are uniform and in|variable. Thus, agreeable to the nature of our

being, it is impossible to doubt concerning the reality of those distinctions and resemblances which we perceive in the bodies that surround us. We may, therefore, conclude, without he|sitation, that man holds the first rank in the or|der of nature; and that brute animals hold the second, vegetables the third, and minerals the last. Though we are unable clearly to distin|guish between our animal and spiritual qualities; though the brute creation are endowed with the same senses, the same principles of life and mo|tion, and perform many actions in a manner si|milar to those of man; yet they have not the same extent of relation to external objects; and, consequently, their resemblance to us fails in numberless particulars. We differ still more from vegetables; but we are more analogous to them than to minerals; for vegetables possess a species of animated organization; but minerals have nothing that approaches to regular organs.

Before we give the history of an animal, it is necessary to have an exact knowledge of the ge|neral order of his peculiar relations, and then to distinguish those relations which he has in com|mon with vegetables and with minerals. An animal possesses nothing common to the mineral, but the general properties of matter: His na|ture and oeconomy, however, are perfectly dif|ferent. The mineral is inactive, insensible, sub|ject to every impulse, without organization, or the power of reproduction, a rude mass, fitted only to be trode by the feet of men and of ani|mals.

Even the most precious metals, which derive their value only from the conventions of men, are regarded in no other light by the phi|losopher. In the animal, the whole powers of nature are united. The principles with which he is animated are peculiar to him: He wills; he determines; he acts; he communicates, by his senses, with the most distant objects; his body is a world in miniature, a central point to which every thing in the universe is connected. These are his peculiar and invariable relations: The faculties of growth and developement, of reproduction and the multiplication of his spe|cies, he possesses in common with the vegetable kingdom.

Progressive motion appears to be the most distinguishing quality between an animal and a vegetable. We, indeed, know no vegetable that enjoys a progressive motion. But this mo|tion is denied to several species of animals, as oysters* 1.2, gall-insects, &c. This distinction, there|fore, is neither general nor essential.

Sensation more essentially distinguishes ani|mals from vegetables. But sensation is a com|plex idea, and requires some explication; for, if sensation implied no more than motion conse|quent upon a stroke or an impulse, the sensitive plant enjoys this power. But, if by sensation we mean the faculty of perceiving and of com|paring ideas, it is uncertain whether brute ani|mals

are endowed with it. If it should be al|lowed to dogs, elephants, &c. whose actions seem to proceed from motives similar to those by which men are actuated, it must be denied to many species of animals, particularly to those that appear not to possess the faculty of progres|sive motion. If the sensation of an oyster, for example, differed only in degree from that of a dog, why do we not ascribe the same sensation to vegetables, though in a degree still inferior? This distinction, therefore, between the animal and vegetable, is neither sufficiently general nor determined.

A third distinction has been derived from the manner of feeding. Animals have organs of apprehension by which they lay hold of their food; they search for pasture, and have a choice in their aliment. But plants are under the ne|cessity of receiving such nourishment as the soil affords them, without exerting any choice in the species of their food, or in the manner of ac|quiring it: The moisture of the earth is the on|ly source of their nourishment. However, if we attend to the organization and action of the roots and leaves, we shall soon be convinced, that these are the external organs by which ve|getables are enabled to extract their food; that the roots turn aside from a vein of bad earth, or from any obstacle which they meet with, in search of a better soil; and that they split and separate their sibres in different directions, and

even change their form, in order to procure nourishment to the plant. A general distinction, therefore, between the animal and vegetable, cannot be founded on their manner of feeding.

From this investigation we are led to conclude, that there is no absolute and essential distinction between the animal and vegetable kingdoms; but that nature proceeds by imperceptible degrees from the most perfect to the most imperfect ani|mal, and from that to the vegetable: Hence the fresh water polypus may be regarded as the last of animals, and the first of plants.

After examining the distinctions, we shall now inquire into the resemblances which take place betwee animals and vegetables. The power of reproduction is common to the two kingdoms, and is a resemblance both universal and essential. This mutual faculty would induce us to think that animals and vegetables are beings of the same order.

A second resemblance may be derived from the expansion of their parts, which is likewise a common property; for vegetables grow as well as animals; and, though some difference in the manner of expansion may be remarked, it is nei|ther general nor essential; since the growth of some considerable parts of animals, as the bones, the hairs, the nails, the horns, &c. is the effect of a genuine vegetation; and the foetus, in its first formation, may be rather said to vegetate than to live.

A third resemblance arises from the following fact: Some animals are propagated in the same manner, and by the same means, as vegetables. The multiplication of the vine-fretter, (puceron), which is effected without copulation, is similar to that of plants by seed; and the multiplication of the polypus by cutting resembles that of plants by slips.

We may now conclude, therefore, with more certainty, that animals and vegetables are beings of the same order, and that Nature passes from the one to the other by imperceptible degrees; since the properties in which they resemble each other are universal and essential, while those by which they are distinguished are limited and par|ticular.

Let us next proceed to compare animals and vegetables in different points of view; for ex|ample, with regard to number, situation, mag|nitude, figure, &c. from which new inductions will arise.

Animals exceed plants in the number of spe|cies. In the class of insects alone, there are, perhaps, a greater number of species, than of the whole species of plants on the face of the earth. Animals differ from each other much more than plants: It is the great similarity of plants that has given rise to the difficulty of distinguishing and arranging them, and to the variety of bo|tanical systems, which are much more numerous than those of zoology.

Beside being more strongly characterised, e|very species of animal is distinguishable from another by copulation. Those may be regarded as of the same species which, by copulation, u|niformly produce and perpetuate beings every way similar to their parents; and those which, by the same means, either produce nothing, or dissimilar beings, may be considered as of diffe|rent species. A fox, for example, will be of a different species from a dog, if nothing results from the intercourse of a male and a female of these two animals; or, if the result be a dissimilar creature, a kind of mule, as this mule cannot multiply, it will be a sufficient demonstration that the fox and dog are different species of ani|mals. In plants we have not the same advan|tage; for, though sexes have been attributed to them, and generic distinctions have been found|ed on the parts of fructification; yet, as these characteristics are neither so certain nor so ap|parent as in animals; and, as the reproduction of plants can be accomplished by several methods which have no dependence on sexes, or the parts of fructification, this opinion has not been suc|cessful; and it is only by the misapplication of an analogy, that the sexual system has been pretended to be sufficient to enable us to distin|guish the different species of the vegetable king|dom.

Though the species of animals be more nume|rous than those of plants, the number of indi|viduals

in each species of the latter far exceed those of the former. In animals, as well as in plants, the number of individuals is much great|er in the small than in the large kinds. Flies are infinitely more numerous than elephants; and there are more herbs than trees. But, if we compare the quantity of individuals in each spe|cies, the number of the plant far exceeds that of the animal. Quadrupeds, for example, produce but few at a time, and at considerable intervals. Trees, on the contrary, produce annually an a|mazing quantity of seeds. It may be alledged, that, to render this comparison exact, the quan|tity of seeds produced by a tree should be com|pared with the quantity of germs contained in the semen of an animal; and then, perhaps, it would appear, that animals abound more in germs than vegetables. But, by collecting and sowing the seeds of a single elm tree, 100,000 young elms may be raised from the product of one year. Though a horse, however, were fur|nished with all the mares he could cover in a year, the result between the production of the animal and of the plant would be very different. I avoid taking notice of the quantity of germs; because of these, especially in the animal, we have no certain knowledge, and because the same seminal germs may exist in the vegetable; for the seed of a plant is not a germ, but a produc|tion as perfect as the foetus of an animal, and

which, like a foetus, requires only the expansion of its parts.

To this may be opposed the prodigious mul|tiplication of some kinds of insects, as the bee, a single female of which will produce 30 or 40 thousand. But, it ought to be remarked, that I am here speaking in general of animals com|pared with vegetables. Besides, the bee, which affords, perhaps, an example of the greatest multiplication among animals, proves nothing a|gainst the present doctrine; for, out of 30 or 40 thousand flies produced by the mother-bee, there are but very few females, 1500 or 2000 males; and all the rest are of neither sex, and to|tally incapable of procreating.

It must be acknowledged, that some species of insects, fishes, and shell-animals, appear to be extremely prolific. Oysters, herrings, fleas, &c. are perhaps equally fertile as mosses, and the most common plants. But, in general, most species of animals are less prolific than plants; and, upon comparing the multiplication of the different species of plants, we find not such re|markable differences, with regard to number, as take place among animals. Some animals pro|duce great numbers, and others very few. But, in every species of plants, the quantity produced is always great.

From what we have already observed, it ap|pears, that, both in the animal and vegetable kingdoms, the smallest and most contemptible

species are the most prolific. In proportion as animals seem to be more perfect, the number of individuals decreases. Does the production of particular forms of body, necessary for the per|fecting of sentiment, as those of quadrupeds, and of birds, cost nature more expence of organic particles than the production of inferior crea|tures?

Let us now compare animals and vegetables with regard to situation, size, and figure. Ve|getables can exist no where but on the earth. Most of them are attached to the soil by roots: Some, as truffles, are entirely covered with the soil; and a few grow under water. But the whole require a connection with the surface of the earth. Animals, on the contrary, are more generally diffused. Some inhabit the surface, and others the interior parts of the earth. Some ne|ver rise above the bottom of the ocean, and o|thers swim in the waters. The air, the internal parts of plants, the bodies of men and of other animals, and even stones themselves, are stored with inhabitants.

By the assistance of the microscope, many new species of animals have been discovered. But, what is singular, we are not indebted to this in|strument for above one or two species of plants. The small moss, of which mouldiness consists, is perhaps the only microscopic plant which has been described. From this it would appear, that Nature has refused existence to very small plants,

while she has created animalcules in the greatest profusion. But this opinion should not be a|dopted without examination. Plants are so si|milar in their structure, that it is much more difficult to distinguish them than animals. This mouldiness, which we imagine to be only a very small moss, may be a forest or a garden consist|ing of a multitude of different plants, though we are unable to distinguish them.

Animals and vegetables differ also with regard to size. There is a greater disproportion between the bulk of a whale and that of one of these pre|tended microscopic animals, than between the largest oak and the small moss mentioned above. Though bulk be only a relative attribute, it may be useful to know the limits within which na|ture has confined her productions. As to large|ness, plants differ but little from animals. The quantity of matter in a whale and in a large tree is nearly equal; but, as to smallness, some men have pretended to have seen animals so extreme|ly minute, that a million of them collected in a heap, would not equal the small moss on a piece of mouldy bread.

The most general and most obvious distinc|tion between plants and animals arises from their figure. The form of animals, though infinitely various, has no resemblance to that of plants: And, though the polypi, which, like plants, can be multiplied by cuttings, may be regarded as the link which connects the animal and vege|table

kingdoms, not only from the manner of their reproduction, but still more from their fi|gure; yet there is no danger of mistaking the one for the other. The operations of some ani|mals resemble plants or flowers. But plants ne|ver produce any thing similar to an animal; and those wonderful insects which make corals, would never have been mistaken for flowers, if, by a foolish prejudice, coral had not been re|garded as a plant. Thus the errors we may commit in comparing plants and animals, are confined to a few objects which lie on the ex|tremities of the two kingdoms; and the farther we extend our observations, we shall be the more convinced, that the Creator has instituted no fixed limits between the animal and vegetable; that these two species of organized beings pos|sess a greater number of common properties than of real differences; that the production of an animal requires, perhaps, a smaller exertion of Nature than the production of a vegetable; or rather, that the production of organized bodies requires no immediate exertion at all; and, lastly, that animation, or the principle of life, instead of a metaphysical step in the scale of be|ing, is a physical property common to all matter.

CHAPTER II.

Of Reproduction in general.

WE shall now more closely examine this property common to the animal and vegetable; this faculty of producing beings si|milar to themselves; this successive chain of in|dividuals which constitutes the real existence of the species: And, without limiting our research to the generation of man, or of any particular animal, let us contemplate the general phaeno|mena of reproduction; let us collect facts, and enumerate the various methods employed by Nature for the renovation and transmission of organized existences.

The first, and apparently the most simple me|thod, is to assemble in one body an infinite num|ber of similar organic bodies, and to compose its substance in such a manner, that every part shall contain a germ or embryo of the same species, and which might become a whole of the same kind with that of which it constitutes a part* 1.3.

This apparatus appears, at first sight, to suppose a profusion of expence. Such magnificence, however, is not uncommon in Nature. It is dis|cernible even in the more common and inferior species, as in worms, polypi, elms, willows, and many other plants and insects, every part of which contains a whole, and, in order to become a plant or an insect, requires only to be unfold|ed or expanded. Considering organized bodies under this point of view, an individual is a whole uniformly constructed in all parts, a col|lection of an infinite number of particles every way similar, an assemblage of germs or minute individuals of the same species, which, in certain circumstances, are capable of being expanded, and of becoming new beings like those from which they were originally separated.

This idea, when traced to the bottom, disco|vers a relation between animals, vegetables, and minerals, which we would not have suspected. Salts, and some other minerals, consist of parts similar to one another, and to the whole. A grain of sea-salt, as we distinctly perceive by the microscope, is a cube composed of an infinite number of smaller cubes* 1.4, which, as we disco|ver

by a larger magnifier, are themselves com|posed of still smaller cubes. The primitive and constituent particles of this salt must, therefore, unquestionably consist of cubes so minute, that they will for ever escape our observation. Plants and animals, which possess the power of multi|plying by all their parts, are organized bodies composed of similar organic bodies, the primi|tive and constituent particles of which are also organic and similar. Of these we discern the accumulated quantity; but we can only recog|nise the constituent particles by reason and ana|logy.

From this view, we are led to conclude, that there exists in nature an infinity of organic, li|ving particles* 1.5, of the same substance with orga|nized beings. A similar structure we have al|ready remarked in more inanimated matter, which is composed of an infinite number of mi|nute particles that have an exact resemblance to the whole body. And, as the accumulation perhaps of millions of cubes are necessary to the

formation of a single grain of sea-salt that is per|ceptible by our senses, an equal number of simi|lar organic particles are requisite to produce one of those numberless germs contained in an elm, or in a polypus. A cube of sea-salt must be dis|solved before we can discover, by means of crystallization, the minute cubes of which it is composed: In the same manner, the parts of an elm or of a polypus must be separated, before we can recognise, by means of vegetation, or ex|pansion, the small elms or polypi contained in the different parts of these bodies.

The difficulty of assenting to this idea proceeds from the well known prejudice, that we can on|ly judge of the compound by the simple; that, to discover the organic structure of any being, it must first be reduced to its simple and unorganic parts; and that hence it is more easy to conceive how a cube must necessarily be com|posed of other cubes, than how a polypus can be composed of other polypi. But, if we ex|amine attentively what is meaned by simple and compound, we shall find, that in this, as in every thing else, the plan of Nature is very different from the grossness and imperfection of our con|ceptions.

Our senses, it is well known, convey not to us exact representations of external objects. When we want to calculate, to judge, to com|pare, to weigh, to measure, &c. we are obliged to have recourse to foreign aid, to rules, to prin|ciples,

to usages, to instruments, &c. All these adminicles are efforts of human genius, and be|long more or less to the abstraction of our ideas. This abstraction, with regard to us, constitutes the simplicity of things; and the difficulty of re|ducing them to this abstraction is the compound. Extension, for example, being a general and ab|stract property of matter, is not much com|pounded. In order, however, to judge concern|ing it, we have imagined some extensions to have no thickness, others to have neither thick|ness nor breadth, and points, which are exten|sions without being extended. All these abstrac|tions have been invented as supports to the un|derstanding; and the few definitions employed in geometry have given rise to numberless pre|judices and false conceptions. Whatever is re|ducible under any of these definitions is called simple; and such things as cannot be easily re|duced to this standard are considered as complex. Thus, a triangle, a square, a circle, a cube, and all those curves of which we know the geome|trical properties, are regarded as simple. But every thing which we cannot reduce under these sigures, or abstract rules, appears to us to be com|plex. We never reflect, that all these geometri|cal sigures exist no where but in our own ima|ginations, or that, if they are ever found in Na|ture, it is only because she exhibits every pos|sible form; and the appearance of simple figures, as an exact cube, or an equilateral pyramid, is,

perhaps, more difficult and rare to be found in nature, than the complex forms of plants or of animals. It is in this manner that we perpetu|ally consider the abstract as simple, and the real as complex. But, in nature, no abstract exists; nothing is simple; every object is compounded. We are unable to penetrate into the intimate structure of bodies. We cannot, therefore, de|termine what objects are more or less complex, unless by the greater or less relation they have to ourselves, and to the rest of the universe. For this reason, we regard the animal as being more complex than the vegetable, and the vegetable than the mineral. With respect to us, this no|tion is just; but we know not whether the ani|mal, vegetable, or mineral, be, in reality, the most complex or the most simple; and we are igno|rant whether the production of a globe or a cube requires a greater effort of Nature than that of a germ, or an organic particle. If we were to indulge in conjectures upon this subject, we might imagine the most common and most nu|merous objects to be the most simple. But this would make animals more simple than plants or minerals, because the former exceed the latter in number of species.

But, without dwelling longer on this subject, it is sufficient to have shown, that all our no|tions concerning simple and compound are ab|stract ideas; that they cannot be applied to the complex operations of nature; that, when we

attempt to reduce all bodies into elements of a cubical, prismatic, globular, or any other regular figure, we substitute our own imaginations in opposition to real existences; and that the forms of the constituent particles of different bodies are absolutely unknown to us; and, of course, we may believe or suppose that organized beings are composed of similar organic particles, as well as that a cube consists of other cubes. We have no other method of judging but by experience. We know that a cube of sea-salt is composed of many lesser cubes, and that an elm consists of a great number of minute elms; because, if we take a piece of a branch, of a root, of the wood separated from the trunk, or a seed, from all these a new tree is produced. The polypus, and some other species of animals, may likewise be multiplied by cuttings separated from any part of their bodies; and, as our rule of judging in both cases is the same, why should we form a different opinion concerning them?

The above reasoning renders it extremely probable, that there really exists in nature an infinite number of small organized beings, every way similar to those large organized bodies which make such a conspicuous figure in this world; that these small organized beings are composed of living organic particles, which are common both to animals and vegetables, and are their primary and incorruptible elements; that an assemblage of these particles constitutes an

animal or a plant; and, consequently, that re|production or generation is nothing but a change of form, effected solely by the addition of simi|lar particles; and the death, or resolution of organized bodies, is only a separation of the same particles. Of the truth of this doctrine, not a doubt will remain, after the proofs de|livered in the following chapters are perused. Besides, if we reflect on the growth of trees, and consider what an immense mass is produced from so small an origin, we must be persuaded that this increase of matter is effected by the simple addi|tion of organic particles which are similar to one another, and to the whole. The seed first pro|duces a small tree, which it contains in minia|ture within its coats. At the top of this small tree a bud is formed, which contains the tree that is to spring the next season; and this bud is an organized body similar to the small tree of the preceding year. The small tree of the se|cond year, in the same manner, produces a bud which contains a tree for the third year; and this process uniformly goes on as long as the tree continues to vegetate: Buds are likewise formed at the extremity of each branch, which contain, in miniature, trees similar to that of the first year. It is evident, therefore, that trees are composed of minute organized bodies similar to themselves, and that the whole individual is formed by a numerous assemblage of minute and similar individuals.

But, it may be demanded, were not all these minute, and similarly organized bodies, contain|ed in the seed? and may not the order of their unfolding be traced from that source? for it is apparent, that the first bud was surmounted by a similar bud, which was not expanded till the second year, and the third bud was not unfold|ed till the third year; and, consequently, the seed may be said to have really contained the whole buds which would be formed for 100 years, or till the dissolution of the plant: It is also appa|rent, that this seed contained not only all the small organized bodies which must in time have constituted the individual tree itself, but like|wise all the seeds, and all the individuals which would successively arise, till the final destruction of the species.

This, indeed, is a capital difficulty; and we shall therefore examine it with the greater at|tention. It is true, that the seed produced a small tree the first year, solely by the unfolding of the bud or germ which it contained, and that this small tree existed in miniature in the bud. But it is not equally certain that the bud of the second year, and those of the succeeding years, nor that all the small organic bodies, and the seeds which must have been formed till the end of the world, or the destruction of the species, were contained in the first seed. This opinion supposes an infinite progression, and makes every individual a source of eternal generations. The

first seed, for instance, must have included all the plants of its species which have existed, or ever will exist; and the first man must have contained in his loins all the men who have ap|peared, or will appear, on the face of the earth. Every seed, and every animal, according to this doctrine, must have included in its own body an infinite posterity. If we yield to reasonings of this kind, we must lose sight of truth in the labyringths of infinity; and, in place of solving, or of throwing light upon the question, we will involve it in tenfold obscurity. It is removing the object beyond the reach of our vision, and then complaining that we cannot see it.

Let us investigate the nature of the ideas of infinite progression and expansion. How do we acquire them? In what do they instruct us? We derive the idea of infinity from the idea of what is limited. It is in this manner we obtain the ideas of infinite succession, and geometrical infi|nity: Every individual is a unit; several indivi|duals make a limited number; and a whole spe|cies is to us an infinite multitude. From the same data which we have demonstrated the non|entity of geometrical infinity, we might prove, that infinite succession, or propagation, rests on no firmer basis; that it is only an abstract idea, a mere deduction from the idea of finite objects, by lopping off the limits which necessarily ter|minate every magnitude* 1.6; and, of course, that

every opinion which infallibly leads to the idea of actual existence, upon no better authority than what is derived from geometrical or nume|rical infinity, ought to be rejected.

The partizans of this opinion are now redu|ced to the necessity of acknowledging, that their infinity of succession and of multiplica|tion is only an indeterminable or indefinite number. But, say they, the first seed, of an elm for example, which weighs not a grain, actually contains all the organic particles requi|site for the formation of this tree, and of all the individuals of the same species which shall ever appear. Is this a solution of the difficulty? Is it not cutting the knot, in place of untying it?

When, is reply to the question, how beings are multiplied? it is answered, that the multi|plication was compleated in the creation of the first individuals, is not this both an acknow|ledgment of ignorance, and a renouncing of all desire of farther improvement? We ask how one being produces its like? and we receive for answer, that the whole was created at once. A strange solution; for, whether only one or a thousand generations had passed, the same diffi|culty remains, and, instead of removing it, the supposition of an indefinite number of germs, all existing and contained in a single germ, increa|ses and renders it altogether incomprehensible.

I allow, that it is much easier to find fault, than to investigate truth, and that the question

concerning reproduction is perhaps of such a subtile nature, as not to admit of a full and satis|factory explication. But we ought at least to inquire whether it be altogether inscrutable; and, in the course of this inquiry, we will discover all that can be known, and the reason why we can know no more.

Questions or inquiries are of two kinds; the first regard primary causes, the other particular effects. If, for example, it be asked why mat|ter is impenetrable? we must either return no answer, or reply by saying, that matter is impenetrable, because it is impenetrable. The same answer must be made, if we inquire into the cause of gravity, of extension, of the inertia of bodies, or of any general quality of matter. Such is the nature of all general and abstract qualities, that, having no mode of com|paring them with other objects in which they do not exist, we are totally incapable of reason|ing concerning them; and therefore all inqui|ries of this kind, being beyond the powers of human intellect, are perfectly uselesss.

But, on the other hand, if the reason of par|ticular effects be demanded, we are always in a condition to give a distinct answer, whenever we can show that these effects are produced by one of the general causes; and the question is equal|ly solved, whether the particular effect proceeds immediately from a general cause, or from a

chain of successive effects, provided we have a clear conception of the dependence of these ef|fects upon each other, and of their mutual rela|tions.

But, when a particular effect appears not to have any dependence upon more general effects, or has no analogy to effects already known, we are then totally unable to give any explication of it; because we have no similar object with which it can be compared. We cannot explain a general cause, because it equally exists in every object; and, on the contrary, we can give no account of a singular or isolated effect; because the same qualities exist not in any other subject. To explain a general cause, we must discover one still more general; but a singular and detached effect may be illustrated by the discovery of an analogous effect, which experience or accident may exhibit.

There is still another kind of question, which may be called a question of fact. For example, why do trees, dogs, &c. exist? All questions of this kind are perfectly insoluble; for those who solve them by final causes consider not that they mistake the effect for the cause: The relation of particular objects to ourselves has no connection with their origin. Moral affinity or fitness can never become a physical reason.

Questions in which we employ the word Why, ought to be carefully distinguished from those

in which we employ How, and still more from those in which we ought to use the words how much or how many. Why always relates to the cause of the effect, or to the effect itself; how re|lates to the manner in which the effect happens; and how much relates to the measure or quantity of the effect.

These distinctions being established, let us now examine the question concerning the reproduc|tion of beings. If it be demanded why animals and vegetables continue their species? we clear|ly perceive that this is a question of fact, and therefore that it is useless and insolvable. But, if it be asked how animals and vegetables are re|produced? we are enabled to solve the question, by giving the history of the generation of every species of animal, and of the reproduction of e|very species of plant: After tracing, however, every possible method of propagation, and ma|king the most exact observations, we have only learned the facts; but have not discovered the causes: And, as the means Nature employs in multiplying and continuing the species, seem to have no relation to the effects produced, we are still under the necessity of asking, by what secret cause she enables beings to propagate their kinds?

This question is very different from the first and second. It admits of nice scrutiny, and e|ven allows us to employ the powers of imagina|tion. It is, therefore, by no means insolvable;

for it belongs not to a general cause. Neither is it solely a question of fact: And, if we can conceive a method of reproduction, depending on primary causes, or which, at least, is not re|pugnant to them, we ought to be satisfied with it; and the more relation it has to the other ef|fects of Nature, it will rest upon a firmer basis.

By the nature of the question, then, we are permitted to form hypotheses, and to chuse that which appears to have the greatest analogy to the other phaenomena of nature. But we ought to reject every hypothesis which supposes the thing to be already accomplished, such, for example, as that which supposes the first germ to contain all the germs of the same species, or that every reproduction is a new creation, an immediate effect of the will of the Deity; for all hypo|theses of this kind are mere matters of fact, con|cerning which it is impossible to reason. We must likewise reject every hypothesis which is founded on final causes, such as, that reproduc|tion is ordained in order to replace the living for the dead; that the earth may always be co|vered with vegetables and peopled with animals; that men may be supplied with abundance of nourishment, &c.; for such hypotheses, in place of explaining the effect by physical causes, stand on no other foundation than arbitrary relations and moral affinities. We ought, at the same time, to despise those general axioms and phy|sical problems so frequently and so injudicious|ly

employed as principles by some philosophers, such as, `Nulla foecundatio extra corpus;' e|very living creature proceeds from an egg; ge|neration always supposes sexes, &c. These max|ims must not be taken in an absolute sense; they signify no more than that the thing happens more commonly in this manner than in any o|ther.

Let us, then, endeavour to find an hypothesis that will be liable to none of these defects or in|cumbrances; and, if we shall not succeed in ex|plaining the mechanism employed by Nature for the reproduction of beings, we shall, at least, be able to approach nearer to the truth than we have hitherto arrived.

In the same manner as we make moulds by which we can bestow on the external parts of bodies whatever figure we please, let us suppose, that Nature can form moulds by which she bestows on bodies both an external and internal figure; would not this be one method by which reproduction might be effected?

Let us first consider whether this supposition be well founded; let us examine whether it contains any thing that is absurd or contradic|tory; and then we shall discover what conse|quences may be drawn from it. Though our senses reach not beyond the external parts of bodies, we have clear ideas of their different si|gures and external affections, and we can imi|tate Nature, by representing external figures in

different ways, as by painting, by sculpture, and by moulds. But, though our senses be limited to external qualities, we know that bodies pos|sess internal qualities, some of which are general, as gravity. This quality or power acts not in proportion to the surfaces, but to the masses, or quantities of matter. Thus, there are in Nature powers, and even of the most active kind, which penetrate the internal parts of matter. We are unable to form distinct ideas of such qualities; because, not being external, they fall not under the cognisance of our senses. But we can com|pare their effects, and may draw analogies from them, in order to account for the effects of simi|lar qualities.

If our eyes, in place of representing to us only the surfaces of bodies, were so constructed as to perceive their internal parts alone, we should then have clear ideas of the latter, without knowing any thing of the former. Upon this supposition, moulds for the internal constitution, which I have supposed to be employed by Nature, would be equal|ly obvious and easy to conceive as moulds for the external figures of bodies; and we should then be in a condition to imitate the internal parts of bodies, as we now imitate the external. These internal moulds, though beyond our reach, may be in the possession of Nature, as she endows bodies with gravity, which penetrates every par|ticle of matter. The supposition of internal moulds being thus founded on analogy, let us

next examine whether it involves any contradic|tion.

It may be alledged, that the expression, inter|nal mould, includes two opposite and contradic|tory ideas; for the idea of a mould relates only to the furface; but the idea of internal, as here em|ployed, has a relation to the whole mass; and therefore we might, with equal propriety, talk of a massy furface as of an internal mould.

I allow, that, when ideas are attempted to be represented which have never been expressed, we are sometimes obliged to use terms that are apparently contradictory. To avoid this incon|venience, philosophers have been accustomed to employ unusual terms, in place of those which have a received signification. But this artifice is of no use, when we can show, that the seem|ing contradiction lies in the words, and not in the idea. But a simple idea cannot include a contradiction; i. e. whenever we can form an idea of a thing, if this idea be simple, it cannot be complex; it can include no other idea; and, of course, it can contain nothing that is opposite or contradictory.

Simple ideas are not only the first apprehen|sions received by the senses, but the first com|parisons which we form of these apprehensions: For the first apprehension is always the result of comparison. The idea of the largeness or di|stance of an object necessarily implies a compa|rison with bulk or distance in general. Thus,

when a idea includes nothing more than com|parison, it ought to be regarded as simple; and, consequently, it can contain nothing contradic|tory. The idea of an internal mould is of this species. There is in nature a quality known by the name of gravity, which penetrates the in|ternal parts of bodies. I understand the idea of an internal mould to be relative to gravity; and, therefore, as it includes only a comparison, it can imply no contradiction.

Let us now trace the consequences that may be drawn from this supposition; let us likewise investigate such facts as may correspond with it; and the more analogies we can collect, the sup|position will be rendered the more probable. We shall begin with unfolding the idea of external moulds, and how it may lead us to conceive the mode of reproduction.

Nature, in general, appears to have a greater bias towards life than death: She seems anxious to organize bodies as much as possible. Of this the multiplication of germs, which may be in|finitely increased, is a convincing proof; and it may be safely affirmed, that, if all matter is not organized, it is only because organized beings destroy one another; for we can increase, at pleasure, the number of animals and vegetables; but we cannot augment the quantity of stones or of dead matter. This appears to indicate, that the most ordinary and familiar operation of Na|ture

is the production of organized bodies; and here her power knows no limitation.

To render this more plain, we shall calculate what may be produced by a single germ. The seed of an elm, which weighs not above the hun|dredth part of an ounce, will, in 100 years, form a tree, of which the mass will amount to ten cubic fathoms. But, at the tenth year, this elm will have produced 1000 seeds, each of which, in 100 years more, will consist of ten cubic fathoms. Thus, in the space of 110 years, more than 10,000 cubic fathoms of organized matter are produced. Ten years after, we shall have ten million of fathoms, without including the annu|al increase of 10,000, which would amount to 100,000 more; and, in ten years more, the num|ber of cubic fathoms would be 10,000,000,000,000. Hence, in 130 years, a single germ would pro|duce a mass of organized matter equal to 1000 cubic leagues; for a cubic league contains only about 10,000,000,000 cubic fathoms; ten years after, this mass would be increased to a thousand times a thousand leagues, or one million of cu|bic leagues; and, in ten more, it would amount to 1,000,000,000,000 cubic leagues; so that, in the space of 150 years, the whole globe might be converted into organized matter of a single species. Nature would know no bounds in the production of organized bodies, if her progress were not obstructed by matter which is not sus|ceptible

of organization; and this is a full de|monstration that she has no tendency to increase brute matter; that her sole object is the multi|plication of organized beings; and that, in this operation, she never stops but when irresistible obstacles occur. What we have remarked con|cerning the seed of an elm, may be extended to any other germ; and it would be easy to show, that, by hatching all the eggs which are produ|ced by hens for a course of 30 years, the num|ber of fowls would be so great as to cover the whole surface of the earth.

Calculations of this kind evince the tenden|cy of Nature towards the production of orga|nized bodies, and the facility with which she performs the operation. But I will not stop here. Instead of dividing matter into orga|nized and brute matter, the general division ought to be into living and dead matter. That what is called brute matter is nothing but matter produced by the death of animals and vegetables, might be proven from the enormous quantities of shells, and other relicts of living bodies, which constitute the principal part of stones, marbles, clays, marles, earths, turfs, and other substances that are commonly reckoned brute matter, but are, in reality, composed of decayed animals and vegetables. This doctrine will be farther illustrated by the subsequent remarks, which appear to be well founded.

The great facility and activity of Nature in the production of organized bodies, the existence of infinite numbers of organic particles which constitute life, have been already demonstrated. We now proceed to inquire into the principal causes of death and destruction. In general, beings which have a power of converting matter into their own substances, or of assimilating the parts of other beings, are the greatest destroyers. Fire, for example, which converts almost every species of matter into its own substance, is the greatest source of destruction that we are ac|quainted with. Animals seem to partake of the nature of flame; their internal heat is a species of fire next to flame. Accordingly, animals are the greatest destroyers; and they assimilate and convert into their own substance all bodies which can serve them for nourishment. But, though these two causes of destruction be very conside|rable, and their effects tend perpetually to the destruction of organized bodies, the cause of re|production is infinitely more active and power|ful. It even seems to derive, from destruction itself, fresh powers of multiplying; for assi|milation, which is one cause of death, is, at the same time, a necessary mean of producing life.

The destruction of organized bodies, as has been remarked, is only a separation of the orga|nic particles of which they are composed. These particles continue separate till they be again u|nited

by some active power. But what is this power? It is the power, possessed by animals and vegetables, of assimilating the matter of their food; and is not this the same, or nearly con|nected with the same power which is the cause of reproduction?

CHAP. III.

Of Nutrition and Growth.

AN animal body is a kind of internal mould, in which the nutritive matter is so assi|milated to the whole, that, without changing the order or proportion of the parts, each part receives an augmentation. This increase of bulk has, by some philosophers, been called an expansion or unfolding of the parts; because they fancied they had accounted for the phae|nomenon, by telling us, that the form of an animal in embryo was the same as at full matu|rity, and that, therefore, it was easy to conceive how its parts should be proportionally unfolded and augmented by the addition of accessory matter.

But, how can we have a clear idea of this aug|mentation or expansion, if we consider not the bodies of animals, and each of their parts, as so many internal moulds which receive the acces|sory matter in the order that results from their position and structure? This expansion cannot be effected solely by an addition to the surfaces, but, on the contrary, by an intus-susception, or by penetrating the whole mass; for the size of

the part is augmented proportionally, without changing its form. Hence it is necessary, that the increasing matter must, in some manner or other, intimately penetrate the whole part in all its dimensions: It is equally necessary, that this penetration should be effected in a fixed order and proportion, so that no internal point receive more matter than another; otherwise some parts would be more quickly unfolded than others, which would entirely change their figure. What can thus regulate the accessory matter, and force it to arrive equally and proportionally to every internal point of the body, if we have not re|course to an internal mould?

The bodies of animals and of vegetables, there|fore, consist of internal moulds, which uniform|ly preserve the same figure. But their masses may receive a proportional increase, by the ex|pansion of the moulds in all their dimensions, both internal and external; and this expansion is effected by an intus-susception of an acces|sory and foreign matter, which intimately pe|netrates the whole, and assumes the same form and identity of substance with the matter of the moulds themselves.

But what is the nature of that matter which an animal, or a vegetable, assimilates to its own substance? What bestows on it that force and activity which enables it to penetrate the inter|nal mould? If such a power exists, must it not

be similar to that by which the mould itself is capable of being reproduced?

These three questions include the whole sub|ject, and appear to depend on one another; for it is impossible to explain, in a satisfactory man|ner, the reproduction of animals or vegetables, if we have not a clear idea how the operation of nutrition is performed. Each question, there|fore, demands a separate examination, that we may be enabled to compare their results.

The first, which regards the nature and qua|lities of the nutritive matter, is in part resolved by the preceding reasonings, and shall be clear|ly unfolded in the subsequent chapters. We shall demonstrate, that there are in nature infi|nite numbers of living organic particles; that nature produces them without any expence, because their existence is constant and invariable; that the causes of death only disunite these par|ticles, but do not destroy them. Thus the mat|ter assimilated by an animal or vegetable, is an organic matter of the same nature with that of the animal or vegetable, and, consequently, may augment the size without changing the figure or the qualities of the original moulds; because it has the same qualities and the same form with the matter of which the moulds themselves are composed. Of the quantity of aliment taken by an animal to support its life, and to maintain the vigour of its organs, and of the juices ab|sorbed by the roots and leaves of a plant, a great

part is rejected by transpiration, by secretions, and by other excretories; and a small portion only is retained for the nourishment and expan|sion of the parts. It is extremely probable, that, in the bodies of animals and of vegetables, a se|paration is made between the brute particles of the aliment and the organic; that the former are carried off by the methods just mentioned; that nothing but the organic particles remain; and that they are distributed, by means of some active power, to the different parts, in a proportion so exact, that neither more nor fewer are applied than answer the purposes of nutrition, and of an equal growth and expansion.

As to the second question, What is the nature of that active power, which enables the organic matter to penetrate and combine with the inter|nal mould? It is apparent, from the preceding chapter, that powers exist in nature, like that of gravity, which affect the most internal parts of matter, without having the smallest relation to its external qualities. These powers, as former|ly observed, are beyond the reach of our senses; because their action is exerted upon the intimate structure of bodies. It is evident, therefore, that we can never obtain a clear idea of them, nor of their mode of acting. Their existence, how|ever, is not less certain, than that, by means of them, most natural effects are produced, espe|cially those of nutrition and expansion, which must be owing to a cause which penetrates the

most intimate recesses of the original moulds; for, in the same manner as gravity pervades the whole parts of matter, the power which pushes forward or attracts the organic particles of food, penetrates the internal parts of organized bodies; and, as these bodies have a certain form, which we have distinguished by the appellation of in|ternal moulds, the organic particles, pushed on by the action of this penetrating force, must en|ter in an order relative to this form, and conse|quently cannot alter its figure, but only augment its bulk, and give rise to the growth and expan|sion of organized bodies: And if, in the orga|nized body, thus expanded, there be some par|ticles similar to the whole, both internally and externally, these parts will become the source of reproduction.

Let us now examine the third question, name|ly, Is it not by a similar power that the internal mould itself is reproduced? This power appears to be not only similar, but the very same with that which is the cause of expansion and reproduc|tion; for, in an organized and expanded body, nothing farther is necessary for the reproduction of a new body similar to itself, than that it should contain some particle every way similar to the whole. This particle, at its first separation, will not present to our eyes a sensible figure by which we can compare it with the whole body. But, when separated from the body, and put in a si|tuation to receive proper nourishment, this simi|lar

particle will begin to expand and to exhibit the form of an entire and independent being, of the same species with that from which it was detached. Thus, a willow or a polypus, as they contain a larger proportion of particles similar to the whole, than most other substances, when cut into any indefinite number of pieces, each segment becomes a new body similar to the pa|rent from which it was separated.

Now, in a body of which all the particles are similar to itself, the organization is the most simple, as has been remarked in the first chap|ter; for it is only a repetition of the same form, a congeries of figures similarly organized. It is for this reason that the most simple bodies, the most imperfect species, are most easily and most abundantly reproduced. But, if an organized body contain only few particles similar to itself, as these alone are capable of a second expansion, its power of reproducing will be both more dif|ficult, and more circumscribed as to the number produced. The organization of bodies of this last kind is also more complex, because it pos|sesses fewer parts which are similar to the whole; and, therefore, the more perfectly a body is or|ganized, its power of reproduction will be pro|portionally diminished.

In this manner we discover nourishment, growth, and propagation, to be effects of the same cause. Organized bodies are nourished by the particles of aliment which are similar to them;

they grow or are expanded by absorbing those or|ganic particles which correspond to their own na|ture; and they propagate, because they contain some organic particles similar to themselves. It only remains to examine whether these similar organic particles are extracted from the food, or have a primary and independent existence in the bodies themselves. If we suppose the latter, we recur to the infinity of similar parts or germs contained within each other, an hypothesis which we have already demonstrated to be replete with difficulties and absurdities. We must, therefore, hold, that the similar parts are extracted from the food; and, after what has been said on the sub|ject, we hope to be able to explain the manner of their absorption, and how the more minute organic particles which compose them are u|nited.

We formerly remarked, that the organic parts of food were separated from those which have no analogy to the animal or vegetable, by tran|spiration and other excretions. The first re|main, and serve to expand and nourish the body: But these organic parts must be of very differ|ent species; and, as each part of the body re|ceives only a proper number of those which corre|spond to it, the surplus, it is natural to imagine, will be returned from all parts of the body, and be collected in one or more reservoirs, where they will unite and form small organic bodies similar to the first, and which require nothing but pro|per

circumstances for expanding and becoming new individuals of the same species; for, all parts of the body sending off organic particles similar to those of which themselves are composed, the result of their union must be the production of new organized bodies similar to the original. This being granted, may we not conclude, that this is the reason why organized bodies, during the time of their growth and expansion, are sel|dom or never capable of reproducing; because the growing parts absorb the whole organic par|ticles presented to them, and no surplus being sent from the different parts of the body, pro|pagation becomes, of course, impracticable?

This account of nutrition, and of reproduc|tion, will not, perhaps, be received by those phi|losophers who admit only a certain number of mechanical principles, and reject every thing as false which depends not upon them; and, as the explication now given of nutrition and repro|duction has no connection with any of these principles, they will conclude that it deserves no credit. But I think very differently from these philosophers. In admitting only a few mechanical principles, they consider not how much they contract the bounds of philosophy, and how few phaenomena can, by this narrow method of thinking, be fully expiscated.

The notion of explaining all the appearances in nature upon the principles of mechanism, is, doubtless, a great exertion, and was first attempt|ed

by Des Cartes. But it is, at least, an unte|nible project; and, though it were otherwise, we are unable to put it in execution. These mechanical principles are, the extension of mat|ter, its impenetrability, its motion, its external figure, its divisibility, the communication of mo|tion by impulse, by the action of springs, &c. These ideas we have acquired by our senses, and we regard them as principles, because they are general and common to all matter. But are we certain that matter possesses no other qualities? Ought we not rather to believe that these qua|lities, which we assume for principles, are only modes of perception; and that, if the confor|mation of our senses were different, we would recognize qualities in matter very different from those above enumerated? It is presumptuous to deny every quality to matter but those we are acquainted with. Many general qualities, per|haps, remain to be discovered; and many may exist which will for ever elude human discern|ment. The cause of impulsion, of cohesion, or of any other mechanical principle, will always continue to be equally inscrutable as that of at|traction, or of any other general quality. Hence it may be concluded, that mechanical principles are nothing else than general effects which ex|perience has enabled us to remark in matter; and that, whenever we shall discover, either by reflection, by analogy, or by experience, a new general effect, it will become a new mechanical

principle, which may be employed with equal advantage and certainty as any of those that are already known.

The defect of Aristotle's philosophy was the employing particular effects as causes; and that of Des Cartes consists in the rejection of every cause, but a few general effects. To use nothing as causes but general effects, to endeavour to augment the number of these, and to attempt to generalize particular effects, would constitute the most perfect principles of genuine philosophy.

In my theory of expansion and reproduction, I first admit the mechanical principles, then the penetrating force of gravity, and, from analogy and experience, I have concluded the existence of other penetrating forces peculiar to organized bodies. I have proved by facts, that matter has a strong tendency towards organization; and that there are in nature an infinite number of organic particles. I have, therefore, only gene|ralized particular observations, without advan|cing any thing contrary to mechanical principles, when that term is used in its proper sense, as de|noting the general effects of Nature.

CHAP. IV.

Of the Generation of Animals.

AS the organization of men, and of other animals, is the most perfect, and the most complex, the propagation of them is like|wise most difficult, and the number of indivi|duals is less abundant. I except here such ani|mals as can be multiplied by a separation of their parts, or without the aid of generation, these having been sufficiently treated of in the pre|ceding chapter* 1.7.

But how will the theory delivered in the former chapter apply to the generation of men, and other animals, who are distinguished by sexes? We understand, from what has been said, how every individual may reproduce; but we cannot conceive how two individuals, the one a male, and the other a female, should uniformly produce a third.

Before replying to this objection, I must ob|serve, that the writers on this subject have con|fined their ideas solely to the generation of men and of animals, without attending to the nature

of reproduction in general: And, as the generation of animals is the most complicated species of re|production, they have laboured under great dis|advantages, not only by attacking the most diffi|cult point, but by leaving themselves no subject of comparison to enable them to illustrate the question. To this circumstance I chiefly attri|bute the unsuccessfulness of their attempts. But, by the route I have taken, I am persuaded that I shall be able to give a satisfactory explanation of every species of reproduction.

Let the generation of man serve as an ex|ample. To begin with infancy:

The expansion and growth of the different parts of man's body being effected by the inti|mate penetration of organic particles analogous to each of these parts, all the organic particles, in early life, are absorbed, and entirely employed in unfolding and augmenting his different mem|bers. He has, of course, little or no superflu|ous particles, till his growth be completed. It is for this reason that infants are incapable of pro|pagating. But, when his body has nearly at|tained its full size, he requires not the same quantity of organic particles; the surplus is, therefore, sent from all parts into reservoirs de|stined for their reception. These reservoirs are the testes and seminal vessels. At this very pe|riod, when the growth of the body is nearly finished, puberty commences, and every phae|nomenon attending it discovers a superabundance

of nourishment: The voice changes into a deeper tone; the beard begins to appear, and other parts of the body are covered with hair; the parts destined for generation are suddenly expanded; the seminal fluid fills the reservoirs prepared for its reception; and, without pro|vocation, it escapes from the body during sleep. This superabundance is still more evident in the female: It discovers itself by a periodic evacua|tion, which begins and terminates with the fa|culty of propagating; by a quick increase of the breasts; and by a change in the sexual parts, which shall be afterwards explained* 1.8.

I conceive, then, that the organic particles sent from all parts of the body into the testicles and seminal vessels of the male, and into the ovarium of the female, compose the seminal fluid, which, in either sex, as formerly observed, is a kind of extract from the several parts of the body. These organic particles, instead of uni|ting and forming an individual similar to that in whose body they are contained, as happens in vegetables, and some imperfect animals, cannot accomplish this end without a mixture of the fluids of both sexes. When this mixture is made, if the organic particles of the male exceed those of the female, the result is a male; and, if those of the female most abound, a female is gene|rated. I mean not that the organic particles of the male or of the female could singly produce

individuals: A concurrence or union of both is requisite to accomplish this end. Those small moving bodies, called spermatic animals, which, by the assistance of the microscope, are seen in the seminal fluids of all male animals, are, per|haps, organized substances proceeding from the individual which contains them; but, of them|selves, they are incapable of expansion, or of becoming animals similar to those in whom they exist. We shall afterwards demonstrate, that there are similar animalcules in the seminal fluids of females, and point out the place where this fluid is to be found.

It is probable, that these organic bodies are only the first rudiments of an animal, containing nothing but its essential parts. We shall not en|ter into a detail of proofs on this subject, but content ourselves with remarking, that the or|ganization of these pretended spermatic animals may be very imperfect; or rather, that they have the living organic particles mentioned above, which are common both to vegetables and to animals; or, at most, that they are only the first junction of these particles.

But, to return to our subject. It may be ask|ed, how is it possible that the superfluous orga|nic particles should be detached from all parts of the body, and unite upon the mixture of the male and female fluids? Besides, are we certain that such a mixture takes place? Has it not been mentioned, that the female furnishes no fluid of

this kind? Is it an established fact, that the male fluid enters the uterus? &c.

To the first question I reply, that, if what I had said concerning the penetration of the in|ternal mould by the organic particles, in growth and nutrition, had been properly understood, it would be easy to conceive, that, when these particles are unable to penetrate the parts into which they formerly entered, they must take another rout, and, of course, arrive at some other part, as the testicles and seminal vessels. Every attempt to explain the animal oeco|nomy, and the various motions of the human body, by mechanical principles alone, must be vain and ineffectual; for it is evident, that the circulation of the blood, muscular motion, and other functions of an animated body, cannot be accounted for by impulsion, or by any of the common laws of mechanism. It is equally evi|dent, that growth and reproduction are effects of laws of a different nature. Why, then, do we refuse the existence of penetrating forces which act upon the whole substances of bodies, when we have examples of such powers in gra|vity, in magnetic attraction, in chemical affini|ties? Since, therefore, we are assured by facts, and by a number of constant and uniform ob|servations, that there are powers in nature which act not by impulsion, why are not these powers ranked among mechanical principles? Why do we reject them in the explanation of effects

which they are known to produce? Why are we desirous of employing only the power of impul|sion? Is not this equally absurd as to judge of painting by the touch; to explain the phaeno|mena that belong to the mass by those that relate only to the surface; or to use one sense in place of another? It is limiting the reasoning faculty to a small number of mechanical principles, which are by no means sufficient to explain the various effects of nature.

But, if these penetrating forces be once ad|mitted, is it not natural to imagine, that those par••••••••es which are most analogous to one ano|ther will unite in the most intimate manner; that each part of the body will appropriate those which are most agreeable to its nature; and that the whole superfluous particles will form a semi|nal fluid, which shall contain all the organic ••••r|ticles necessary for forming a small organized body, similar in every respect to that from which the fluid is extracted? May not a force, similar to that which is the cause of growth, be sufficient to collect the superfluous organic particles, and bestow on them the figure of the body from which they proceed?

That our food contains an immense number of organic particles, requires no formal proof; since we are solely nourished by animals and ve|getables, which are organized substances. In the stomach and intestines, the gross parts of the a|liment are separated and rejected by the excre|tories.

The chyle, which is a purer part of the aliment, is absorbed by the lacteal vessels; from thence it is carried into the mass of blood, and, in the course of circulation, it is more and more refined, the unorganic and useless particles being thrown out by transpiration and other se|cretions: But the organic particles are retained, because they are analogous to the blood, and are attracted by it. Hence, as the whole mass of blood passes several times through the body, during the course of this perpetual circula|tion, I suppose, that each particular part attracts those particles which are most analagous to it, and allows the rest to move on. In this manner all the parts are nourished and unfolded, not, as is commonly imagined, by a simple addition of matter to their furfaces, but by an intimate pene|tration of substance, effected by a force which acts equally upon every point of the whole mass: And, after the different parts have acquired their utmost growth, and are fully impregnated with similar organic particles, as their substance becomes then more dense and solid, I imagine that they lose their faculty of attracting and re|ceiving the particles presented to them. But, as the particles continue to be carried round in the course of the circulation, and are no longer ab|sorbed in such quantities as formerly, they must, of necessity, be deposited in some particular re|servoir, such as the testicles and seminal vessels. When this fluid extract of the male is mixed

with that of the female, the particles which are most analogous to each other, being actuated by a penetrating force, unite and form a small or|ganized body, similar to the one or the other sex; and this body, when once formed, requires only an expansion of its parts, an operation which is performed in the womb of the mother.

We shall now consider the second question, namely, whether the female has a seminal fluid similar to that of the male? In the first place, though such a fluid exists in females, the mode of emission is very different from that of the male, being generally confined within the body* 1.9. The antients were so confident of the existence of a female fluid, that they distinguished the two sexes by their different modes of emission. But those physicians who attempt to explain genera|tion by eggs, or by spermatic animalcules, insist, that females have no peculiar fluid; that the mucus issuing from the parts has been mistaken for a seminal fluid; and that the opinion of the antients on this subject is destitute of foundation. This fluid, however, does exist; and the doubts concerning it have arisen solely from attachment to systems, and from the difficulty of discover|ing its reservoir. The fluid which is separated from the glands about the neck and orifice of the uterus, has no visible reservoir; and, as it flows out of the body, it is natural to think that it is

not the prolific fluid, because it cannot co-ope|rate in the formation of the foetus, which is performed within the uterus. The reservoir for the prolific fluid of the female, therefore, must be situ|ated in a different part: It even flows abundant|ly; though, like that of the male, a small quan|tity is sufficient to produce a foetus. If a little of the male fluid enters the uterus, either by its orifice or by absorption, and meets with the smallest drop of the female fluid, it is sufficient for the purpose of propagation. Thus, nei|ther the observations of some anatomists, who maintain that the seminal fluid of the male can have no admission into the uterus, nor the oppo|site opinion maintained by their antagonists, have any influence upon the theory we are en|deavouring to establish. But the discussion of these points we leave to a future opportunity.

Having obviated such objections as might be made, let us attend to the evidences that concur in supporting our hypothesis. The first arises from the analogy between growth and repro|duction. It is impossible to give a satisfactory account of growth or expansion, without having recourse to those penetrating forces, those affini|ties or attractions which we employed in explain|ing the formation of the small organic bodies that are similar to the large bodies which con|tain them. A second analogy is derived from this circumstance, that both nutrition and repro|duction proceed, not only from the same effi|cient,

but from the same material cause, namely, the organic particles of food; and what proves the surplus of the nutritive particles to be the cause of reproduction, is, that the body is not in a condition to propagate till its growth be finish|ed: Of this we have daily examples, in dogs and other animals, who follow, more closely than we do, the laws of nature: They have no in|clination to propagate till they have nearly at|tained their full growth; and by this we know whether the growth of a dog be finished; for he seldom grows after being in a condition to generate.

Another proof that the seminal fluid is form|ed of the surplus of the nutritive particles, arises from the condition of eunuchs and other muti|lated animals: In this unnatural state, animals grow fatter than those who retain all their parts. The superabundance of nutriment, having no organs for its evacuation, changes the whole ha|bit of their bodies. The knees and haunches of eunuchs grow uncommonly large. The rea|son is evident. After their bodies have acquired the common size, if the superfluous organic par|ticles found an issue, as in other men, the growth would proceed no farther. But, as they want organs for emitting the seminal fluid, which is nothing but the superfluous nutritive particles, it remains in the body, and has a constant ten|dency to expand the parts beyond their natural size. Now, bones, it is well known, grow or

extend by their extremities, which are soft and spongy, and, when they have once acquired so|lidity, they are incapable of farther extension: Hence the superfluous organic particles can on|ly enlarge the spongy extremities of bones; and this is the reason why the haunches, knees, &c. of eunuchs augment to a disproportioned bulk.

But the strongest proof of the truth of our present doctrine arises from the resemblance of children to their parents. Sons, in general, resemble their fathers more than their mothers, and daughters have a greater resemblance to their mothers than their fathers; because, with regard to the gene|ral habit of body, a man resembles a man more than a woman, and a woman resembles a wo|man more than a man. But, as to particular features or habits, children sometimes resemble the father, sometimes the mother, and sometimes both. A child, for example, will have the eyes of the father, and the mouth of the mother, or the colour of the mother and the stature of the father. Of such phaenomena it is impossible to give any explication, unless we admit that both parents have contributed to the formation of the child, and, consequently, that there has been a mixture of two seminal fluids.

These resemblances long embarrassed me, and, till I had maturely considered the subject of ge|neration, led me into many errors and prejudices: And it was not without much thought, a minute

examination of a great number of families, and a multiplicity of evidence, that I could prevail on myself to alter my former opinion, and to em|brace what I now believe to be truth. But the objections which might occur concerning mulat|toes, mongrels, mules, and particular parental resemblances, instead of opposing my theory, I despair not of being able to show that they strengthen and confirm it.

In youth, the seminal fluid is less copious, but more stimulating. Its quantity continues to augment till a certain age; because, in propor|tion as we approach that age, the parts of the body become more solid, admit fewer nutritive particles, send back more of them to the com|mon reservoirs, and, of course, augment the quantity of the seminal fluid. Thus, if the ex|ternal organs have not been used, middle-aged men, or even old men, procreate with more ease than young men. This is evidently the case with the vegetable tribes: A tree, the older it is, produces the greater quantity of fruit.

Young people, who, by forced irritations, de|termine an unnatural quantity of this fluid into the reservoirs prepared for its reception, imme|diately cease to grow, lose their flesh, and at last fall into consumptions. The reason is apparent: They lose, by premature and too frequent eva|cuations, the very substance which nature in|tended for the nourishment and growth of their bodies.

Men who are thin, but not emaciated, and those who are plump, but not fat, are the most vigorous. Whenever the superabundant nutri|tive particles begin to form fat, it is always at the expence of the seminal fluid and other ge|nerative powers. When the growth of the dif|ferent parts of the body is compleat, when the bones have acquired full solidity, when the car|tilages begin to ossify, and, lastly, when the parts almost refuse the admission of nutritive particles, then the fat augments considerably, and the quantity of seminal fluid diminishes; because the nutritive particles, instead of being sent back to the reservoirs, are arrested in every part of the body.

The quantity of seminal fluid not only in|creases till we arrive at a certain age, but it be|comes more thick. It contains, in the same bounds, a greater quantity of matter. Its specific gravity is nearly double that of the blood; and, of course, it is heavier than any o|ther animal fluid.

To a man in health, an evacuation of this fluid whets the appetite: He soon finds the ne|cessity of repairing the loss by fresh nourish|ment. Hence we may conclude, that abstinence and hunger are the most effectual checks to lux|ury of every kind.

Many other remarks might be made on this subject, which must be deferred till we come to treat of the history of man: We shall, therefore,

conclude with a few observations. Most ani|mals discover no inclination for the sexes till their growth be nearly finished: Those which have but one season in the year, have no semi|nal fluid excepting at that time. Mr Needham* 1.10 not only saw this liquor forming in the milt of the Calmar, but likewise the spermatic animals, and the milt itself, which have no existence till the month of October, when this fish spawns on the coasts of Portugal, where Needham made the observation. After the spawning time is over, the seminal liquor, the spermatic animals, and the milt, dry up and totally disappear; till the same season returns next year, when the superfluous nutritive particles renew the milt as formerly. The history of the deer will furnish us with an opportunity of remarking the various effects of rutting, the most conspicuous of which is the extenuation of the animal; and, in those species of animals whose rutting or spawning happens but once in a year, the extenuation of their bodies is proportionally great.

As women are smaller and weaker than men, as their constitutions are more delicate, and, as they take less food, it is natural to think that their superfluous organic particles should also be less abundant: Of course, their seminal fluid will be weaker and smaller in quantity than that of men; and, since the fluid of females contains fewer organic particles, must not a greater num|ber

of males than of females result from a mix|ture of these two fluids? This is really the case; and to account for it has hitherto been deemed impossible. The number of males born exceeds that of females about a sixteenth part; and we shall afterwards see that the same effect is pro|duced by the same cause in all the different spe|cies of animals.

CHAP. V.

Examination of the different Systems of Generation.

PLATO, in the Timaeus, accounts not only for the generation of men, of animals, of plants, and of the elements, but even of the hea|vens and of the gods themselves, by images reflected or extracted from the divine Creator; which images, by an harmonic movement, are arranged in the most perfect order, according to the properties of number. The universe, he says, is a copy of the Deity; time, space, mo|tion, and matter, are the images or representa|tions of his attributes; and secondary and parti|cular causes are results of the numeric and har|monic qualities of these images: The world, from its excellency, is the most perfect animated being. To give the world complete perfection, it was necessary that it should contain all the o|ther animals, or all the possible forms and representations of the creative power. Man is one of these forms. The essence of all genera|tion consists in the unity and harmony of the number Three, or of the Triangle, namely, that which generates, that in which generation is performed, and the result, or that which is generated. The succession of individuals in the

species, is only a fugitive image of the immu|table eternity of this harmonic triangle, a uni|versal prototype of all existences, and of all ge|nerations.

This philosopher paints only ideas. Disen|gaged from matter, he flies into the regions of abstraction; and, losing sight of sensible objects, he contemplates those of intellect alone. One cause, one end, one mean, compose the whole of his perceptions: God is the cause, perfection the end, and harmonic representations the means. This idea is sublime; the mode of philosophi|sing is noble and full of simplicity; but it is perfectly vacant, and affords no objects for spe|culation. We are not pure intelligences. We are unable to give real existence to our ideas. Chained to matter, or rather depending on the causes of our sensations, it is impossible that we should realise abstractions. To Plato I might reply in his own manner, 'The Creator realises every thing he conceives; his perceptions be|get existence: The created being, on the con|trary, conceives nothing but by retrenching from reality; and annihilation is necessary to bring forth his ideas.'

Let us, without regret, therefore, confine our|selves to a philosophy more humble and more material; and, keeping within the sphere which nature has allotted us, let us examine those rapid and daring spirits who attempt, though in vain, to fly beyond the limits of humanity. The whole

of this Pythagorean philosophy, which is purely intellectual, depends upon two principles, the one false, and the other uncertain; namely, the real power of abstraction, and the natural exist|ence of final causes. To apprehend numbers to be real beings; to say that unity is a general individual, which not only represents all indivi|duals, but even communicates existence to them; to pretend that unity exercises the actual power of engendering another unity nearly resembling itself, and of creating two individuals, two sides of a triangle, that can have no connection or perfection without a third side, which is neces|sarily produced by the other two; in fine, to re|gard numbers, geometrical lines, and metaphy|sical abstractions, as real and efficient physical causes, by which the elements are formed, plants and animals regenerated, and all the phaeno|mena of nature produced, appears to be the greatest and most absurd abuse of human rea|son, and an invincible obstacle to the advance|ment of knowledge. Besides, nothing can be more fallacious than such chimeras. Sup|posing we should agree with Plato and Mal|branche, that matter has no existence, that ex|ternal objects are only ideal images of the crea|tive power, and that we see every thing in the Deity himself; does it follow, that our ideas are of the same order with those of the Creator, and that they can produce real existences? Are we not dependent on our sensations? Whether the

objects which excite sensations be real or imagi|nary, whether they exist without or within, whe|ther it be God or matter that we every where behold, is to us of little importance: We are not less certain of being uniformly affected in the same manner by the same causes. The re|lations between our senses and the objects which affect them, are necessary and invariable. It is upon this basis alone that the principles of phi|losophy ought to be founded, otherwise our knowledge must be useless and fallacious. Can an harmonic triangle create the substance of the elements? Is fire, as Plato affirms, an acute tri|angle, and light and heat two properties of this triangle? Are water and air rectangular and e|quilateral triangles? Is the form of the element of earth a square, because, being the least per|fect of the four elements, it recedes as far as possible from a triangle, without departing alto|gether from its essence? Do males and females embrace each other, for no other purpose but to complete the triangle of generation? These Pla|tonic ideas have two different aspects: In spe|culation, they seem to proceed from sublime principles; but the application of them in prac|tice leads to nothing but false and childish con|clusions.

Is it difficult to perceive that our ideas origi|nate from our senses alone; that the objects we regard as real existences, are those concerning which the senses uniformly give the same testi|mony;

that the objects we apprehend as having a real existence, are those which are invariably presented to us in the same manner; that the mode in which they present themselves has no dependence upon our will or inclination; that, of course, our ideas, instead of being the causes of things, are only particular effects, which be|come less similar to the objects themselves, in proportion as they are rendered more general; and, lastly, that mental abstractions are only ne|gative beings, which derive their intellectual ex|istence from the faculty we possess of consider|ing objects, without regarding their sensible qua|lities

Is it not, therefore, apparent, that abstract i|deas can never be the principles of existence, or of real knowledge? On the contrary, all our knowledge is derived from comparing and ar|ranging the results of our sensations. These re|sults are known by the appellation of experience, the only source of genuine science. The em|ployment of any other principle is an abuse; and every edifice founded upon abstract ideas, is a temple erected to Error.

In philosophy, error has a more extensive in|fluence than in morals. A thing may be false in morals solely because it is misrepresented. But falsehood in metaphysics consists not in misre|presentation alone, but in taking for granted what has no existence at all. It is into this most per|nicious species of error that the Platonists and

the Sceptics have fallen. Their false suppositions have obscured the natural light of truth, bewil|dered the reasoning faculties of men, and retard|ed the progress of philosophy.

Final causes are employed as a second prin|ciple by Plato and other theorists. This prin|ciple has even been adopted by the vulgar, and by some modern philosophers. A moment's re|flection, however, will be sufficient to reduce this principle to its proper value. To say that light exists because we have eyes, and that sounds exist because we have ears; or to say that we have eyes and ears, because light and sounds exist; is not this precisely the same thing? or, rather, are we any wiser by this kind of reason|ing? Will we ever make any discoveries by such a mode of explication? Is it not apparent, that final causes are only arbitrary relations and moral abstractions, which ought to have less in|fluence than abstractions in metaphysics, because the origin of the former is less noble and worse imagined? And, though Leibnitz has endeavour|ed to give an elevation to final causes, under the appellation of the reasonableness and eternal fit|ness of things, [raison suffisante], and Plato has represented them under the flattering picture of absolute perfection; all these efforts are insuffi|cient to cover their native insignificance and precariousness. Are we better instructed in the operations of Nature, because we are told that nothing exists without a reason, or that every

thing is created with a view to the perfection of the whole? What is reasonableness or fitness? What is perfection? Are they not moral beings, created solely by the human intellect? Are they not arbitrary relations which we have contrived to generalise? They have no foundation but in moral affinities, which, so far from producing any physical or real existence, change the nature of truth, and confound the objects of our sen|sations, of our perceptions, and of our under|standings, with those of our sentiments, of our passions, and of our wills* 1.11.

Much more might be said upon this subject. But I pretend not to write a treatise on philo|sophy; and shall therefore return to physics, from which the ideas of Plato, concerning uni|versal generation, have diverted my attention. Aristotle, who was as great a philosopher as Plato, and a better physician, instead of wan|dering in the regions of theory, collects facts, and speaks in a language more intelligible.

Matter, he remarks, which is only a capacity of receiving forms, assumes, in generation, a fi|gure similar to the individual which furnishes it: And, with regard to animals which generate by the intervention of sexes, he imagines, that the prolific principle proceeds solely from the male* 1.12: For though, in another place, when speaking of animals in general, he says, that the female

sheds a seminal fluid within the body, it appears, that he regards not this fluid as a prolific prin|ciple; and yet he tells us, that the menstrual blood serves for the formation, nourishment, and growth of the foetus; but that the efficient principle exists alone in the seminal fluid of the male, which acts not as matter, but as a cause. Averrhoes, Avicenna, and other philosophers who embraced this opinion of Aristotle, have endea|voured to prove that females have no prolific fluid. They alledge, that, as females are fur|nished with a menstrual fluid, which is both necessary and sufficient for the purposes of ge|neration, it is unnatural to suppose them pos|sessed of any other, especially since it begins to appear, like that of the male, at the age of pu|berty. Besides, they continue, if females really have a prolific seminal fluid, why do they not produce without the intercourse of the male, since they contain the prolific principle, as well as the matter necessary for the growth and ex|pansion of the embryo? This last reason is the only one which merits attention. The men|strual blood appears to be necessary for the growth and nourishment of the foetus; but still it may contribute nothing to its first formation, which requires the mixture of both prolific fluids. Females, therefore, like males, may have a prolific fluid for the formation of the embryo, as well as menstrual blood for its growth and nourishment. The imagination is not unnatu|ral,

that, as the female possesses both a prolific fluid extracted from all parts of her body, and likewise the means of expanding and nourish|ing, she should produce females without any communication with the male. It must be al|lowed, that this metaphysical argument used by the Aristotelians for proving that females are destitute of a prolific fluid, may be urged as the strongest argument against every system of ge|neration, and, in particular, against that which I am endeavouring to establish.

Let us suppose, it may be said, that the super|fluous organic particles are sent from every part of the body into the testicles and seminal vessels of the male, why do they not, by means of your imaginary attracting forces, form small organi|zed bodies similar to the whole? Why are not similar bodies generated in the female, without any intercourse with the male? If you answer, that the male fluid contains only males, that the female fluid contains only females, that both pe|rish for want of the circumstances necessary for expansion, and that, for the procreation of an animal, a mixture of both is requisite; may it not be demanded, why this most complicated, difficult, and less fertile mode of generation, is so invariably preferred by Nature, that all animals, with a few trifling exceptions, generate by the mutual commerce of sexes?

I shall content myself, at present, with reply|ing, that this is the mode actually employed by

Nature; and, therefore, however complicated it may appear, it is, in fact, the most simple; be|cause, as I formerly remarked, whatever most frequently happens, is, in itself, however it may seems to us, the most simple.

Besides, the notion of the Aristotelians, that females have no seminal fluid, cannot receive our assent, if we consider the strong resemblance of children to their mothers, and that mules, mu|lattoes, and mongrels of every kind, uniformly resemble the mother more than the father; and, if it be farther considered, that the generating organs of the female, like those of the male, are properly formed for preparing and receiving a seminal fluid, we shall be easily induced to be|lieve the existence of such a fluid, whether it re|sides in the spermatic vessels, the testicles, or the ovaria, or proceeds, by irritation, from the la|cunae of De Graaf, which are situated at the neck and near the orifice of the uterus.

But we must examine Aristotle's ideas more fully, as, of all the antients, this great philosopher has treated the subject of generation in the most extensive manner. He distinguishes animals into three classes: 1. Those that have blood, and, with few exceptions, propagate by copula|tion; 2. Those that have no blood, and, being hermaphrodites, produce of themselves without copulation; and, 3. Those that proceed from putrefaction, and have no parents of any kind. I shall first remark, that this division is exceed|ingly

improper: Though it be true, that ani|mals having blood are distinguished into male and female, it is by no means equally true, that bloodless animals are, for the most part, herma|phrodites: For the only hermaphrodites we know, are land-snails and worms; but we are uncertain whether all shell-animals, and all those which have no blood, be also hermaphrodites. This must be learned from the particular histories of these animals. And, with regard to those that are alledged to proceed from putrefaction, as Aris|totle gives no enumeration of them, many ob|jections occur; for most species which the an|tients believed to proceed from putrefaction, have, by the moderns, been discovered to pro|ceed from eggs.

Aristotle makes a second division of animals, namely, into those who have the faculty of pro|gressive motion, and those who have no such fa|culty. All animals who move, and have blood, are distinguished by sexes: But those which, like oysters, adhere to one place, or hardly move at all, have no sexes, and, in this respect, re|semble plants; and it is only, he observes, from difference in bulk that they have been distin|guished into male and female. It must be ac|knowledged, that we are still uncertain whether shell-animals have sexes: Among oysters, some individuals are fertile, and others not. The fer|tile individuals are distinguished by a delicate edging or border which surround their bodies,

and they are called males* 1.13. Our observations on this subject are extremely limited.

But to proceed. The male, according to A|ristotle, contains the principle of motion, and the female the material part of generation. The organs destined for this purpose are different in different animals. Of these the testicles are the chief in males, and the uterus in females. Qua|drupeds, birds, and cetaceous animals, have tes|ticles; fishes and serpents are deprived of them; but they have two canals for the reception and maturation of the semen: These parts, so essential to generation, are always double both in males and females; and, in the male, they retard the motion of that part of the blood which goes to the formation of semen. This he proves from the example of birds whose testicles swell consi|derably during the season of their amours, but afterwards diminish so greatly that they can hardly be discovered.

All quadrupeds covered with hair, and the ce|taceous fishes, as whales and dolphins, are vivi|parous: But vipers and cartilagious animals are not properly viviparous; because they produce an egg within their own bodies, previous to the exclusion of the live animal. Oviparous ani|mals are of two kinds; those which produce perfect eggs, as birds, lizards, turtles, &c. and those which produce imperfect eggs, as fishes, whose eggs augment and come to perfec|tion

after they have been deposited in the water by the female: And, in every species of ovipa|rous animals, except birds, the females are larger than the males, as in fishes, lizards, &c.

After remarking these general varieties in the animal kingdom, Aristotle begins with exami|ning the opinion of the antient philosophers, that the semen, both of the male and the female, was extracted from all parts of the body; and he dissents from this opinion; because, says he, though children often resemble both father and mother, they sometimes also resemble their grand|fathers. Besides, they resemble their fathers and mothers in the voice, in the hair, in the nails, and in the gate and manner of walking. Now, he proceeds, it is impossible for the semen to come from the hair, from the voice, from the nails, or from any external quality, as that of the mode of walking. Infants, therefore, re|semble not their parents, because the semen proceeds from all parts of the body, but for o|ther reasons. I will not expose the weakness of these arguments; but shall only remark, that this great man appears to have been anxious to differ from the sentiments of former philosophers: And I am persuaded, that, whoever peruses his trea|tise on generation, will discover, that a strong passion for establishing a system different from that of the antients, obliges him uniformly to prefer arguments of little probability, to the

force of proofs, when they stand in opposition to the general principles of his philosophy.

The seminal liquor of the male, according to Aristotle, is secreted from the blood; and the menstrual fluid of the female is likewise a secre|tion from the blood, and the only matter which contributes to generation. Females, he conti|nues, have no other prolific fluid; no mixture, therefore, of male and female fluid takes place: This he attempts to prove by observing, that some women conceive without pleasure; that few emit any fluid during the time of copula|tion; that, in general, those who are brown, and have a masculine air, have no emission; and yet their powers of procreation are not less than those of a fairer complection and more delicate appearance, who emit copiously. Thus, he concludes, women furnish nothing for the pur|poses of generation, but the menstrual blood. This blood is the matter of generation, and the male fluid contributes nothing but the form: The male fluid is the efficient cause, and the prin|ciple of motion; it is to generation what the sculptor is to a block of marble: The seminal fluid is the sculptor, the menstrual blood the marble, and the foetus the figure. The men|strual blood receives from the male semen a kind of soul, which gives it life and motion. This soul is neither material nor immaterial, because it can neither act upon matter, nor augment the menstrual blood, which is the only matter neces|sary

to generation. It is a spirit, says our phi|losopher, similar to that of the element of the stars. The heart is the first production of this soul, which is the cause of its own growth, and of the growth and disposition of all the other members. The menstrual blood contains the capacities of all the parts of the foetus; the soul or spirit of the male semen makes the heart be|gin to act, and communicates to it the powers of bestowing action on the other viscera; and, in this manner, the different parts of the animal are successively unfolded. All this appears clear and luminous to our philosopher. He has only one doubt, namely, whether the blood or the heart is first realized. And of this he doubted not with|out reason; for, though he adopted the opinion that the heart received its existence first, Harvey has since alledged, from arguments similar to those of Aristotle, that the blood, and not the heart, is first realized.

Thus have I given a short view of what A|ristotle has delivered on the subject of genera|tion, and shall leave the reader to consider whe|ther any system of the antients be more obscure, or more absurd, than that which he has endea|voured to establish. His system, however, has been adopted by most men of learning. Har|vey has borrowed many of Aristotle's notions; but he has also adopted some of his own, which are by no means better founded. It is not sur|prising that Aristotle's theory of generation,

which was a result of his system of philosophy, where form and matter are the great principles, where vegetable and sensitive souls are the a|gents of nature, and where final causes are real objects, should have been received in the schools: But it is not a little astonishing to see a physi|cian and an acute observer, like Harvey, carried down the stream, while, at the same time, most philosophers followed the sentiments of Hippo|crates and Galen, which we shall afterwards take notice of.

We mean not to convey a disadvantageous idea of Aristotle by the account we have given of his theory of generation. We might, with equal propriety, judge of Descartes by his trea|tise on man. What these two philosophers have remarked concerning the formation of the foetus should rather be considered in the light of detached observations, or as consequences which each of them drew from their principles of philosophy, than as compleat systems. Aris|totle admits, with Plato, final and efficient causes: The latter are the sensitive and vegetable souls, that give form to matter, which, in itself, is only a capacity of receiving forms: And as, in ge|neration, the female furnishes the greatest quan|tity of matter, and as it was repugnant to his system of final causes, that any effect should be produced by two causes, when one was sufficient for the purpose, he concludes, that the woman alone contains the matter necessary for procrea|tion:

Again, another of his principles was, that matter, in itself, has no form, and that form is a being distinct from matter; he therefore main|tains, that the male furnishes the form, and, of course, that he contributes nothing material.

Descartes, on the contrary, admitted into his philosophy only a few mechanical principles. By these he attempted to explain the formation of the foetus; and he imagined, that he under|stood, and was able to communicate to others, the manner in which a living organized body could be formed by the laws of motion alone. The principles he employed were different from those of Aristotle. But both of them, instead of directing their inquiries to the thing itself, in place of examining it with impartiality, only considered it in relation to their philosophic prin|ciples, which could never be applied with suc|cess to the nature of generation, because it de|pends, as has been already shown, upon very different principles. Descartes, however, admits the existence and necessary concurrence of the seminal fluids of both sexes. He allows that both furnish something material for the purposes of generation; and that the fermentation occasion|ed by a mixture of the two fluids, is the cause of the formation of the foetus.

Hippocrates, who lived about five or six hun|dred years before Aristotle, taught an opinion, which was adopted by Galen, and by most phy|sicians, for many ages. He maintained the ex|istence

of a female fluid; and even that both male and female had two fluids, the one strong and active, the other weaker and more inactive* 1.14. A concurrence of the two stronger fluids produ|ced a male child, and, of the two weaker, a fe|male. Thus, according to Hippocrates, there exist two kinds of seminal fluids both in the male and in the female. This notion he supports in the following manner: Several women, who produced only girls by their first husband, have had boys by their second; and the same thing has often happened to men who have had two wives. Supposing this to be fact, it admits of an easy explanation, without having recourse to two different fluids peculiar to each sex; for the women who had girls only by the first husband, and boys by the second, furnished a greater quantity of particles proper for generation du|ring the first, than the second marriage; or the second husband furnished a greater quantity of generating particles during the time of the se|cond marriage, than the first. If, at the mo|ment of conception, the organic particles of the male are more abundant than those of the fe|male, a male child is the result; and, when the organic particles of the female most abound, a female child is the consequence: It is not, there|fore, surprising, that the husband should be foil|ed with some women, and have the superiority over others.

It is farther alledged by Hippocrates, that the male semen is secreted from the strongest and most essential fluids of the body; and he thus explains the manner in which the secretion is performed: 'Venae et nervi,' says he, 'ab omni corpore in pudendum vergunt, quibus dum ali|quantulum teruntur, et calescunt ac implentur, velut pruritus incidit, ex hoc toti corpori volup|tas ac caliditas accidit; quum vero pudendum teritur et homo movetur, humidum in corpore calescit ac dissunditur, et a motu conquassatur ac spumescit, quemadmodum alii humores omnes conquassati spumescunt.'

'Sic autem in homine ab humido spumescente id quod robustissimum est ac pinguissimum secer|nitur, et ad medullam spinalem venit; tendunt enim in hanc ex omni corpore viae, et dissun|dunt ex cerebro in lumbos ac in totum corpus et in medullam: Et ex ipsa medulla procedunt viae, ut et ad ipsam humidum perferatur et ex ipsa secedat; postquam autem ad hanc medul|lam genitura pervenerit, procedit ad renes, ac enim via tendit per venas; et si renes fuerint exulcerati, aliquando etiam sanguis defertur: A renibus autem transit per medios testes in pu|dendum, procedit autem non qua urina, verum alia ipsi via est illi contigua* 1.15,' &c.

It will, doubtless, be perceived by anatomists, that Hippocrates errs in tracing the route of the seminal fluid. But this affects not his hypothesis,

that the semen proceeds from every part of the body, and particularly from the head; because, he remarks, those who have had the veins be|hind their ears cut, secrete only a weak and often an unfertile semen. The female likewise sheds a seminal fluid sometimes within the uterus, and sometimes without, when the orifice is too open. The male semen enters the uterus and mixes with that of the female; and, as each has two species of fluid, the one strong and the other weak, if both of them furnish the strong kind, a male foetus is the consequence; and, if both furnish only the weak kind, the result is a fe|male: Besides, if in the mixture there are more particles of the male than of the female fluid, the child will resemble the father more than the mother; et c contra. Here we might ask him, what would happen, when the fluid of the one was strong, and that of the other weak? I can|not conceive what reply could be made to this question; and, therefore, we are warranted to reject the opinion of two distinct fluids in each sex as perfectly chimerical.

Let us now attend to his account of the for|mation of the foetus. The seminal fluids first mix in the uterus, and gradually thicken by the heat of the mother. The mixture extracts the spirit of heat, and when too warm, part of the heat escapes into the air. But a cold spirit is likewise conveyed to it by the respiration of the mother: Thus a cold and a hot spirit alternately

enter the mixture, give life to it, and cover its surface with a pellicle, which assumes a round figure, because the spirits acting in the center, expand the matter equally on all sides. I have seen, says this great physician, a foetus of six days old: It was a ball of liquor inclosed in a pellicle. The liquor was reddish; and the pellicle was interspersed with red and colourless vessels. In the middle of it there was a small e|minence, which I apprehended to be the umbi|lical vessels, by which the foetus receives nou|rishment and the spirit of respiration from the mother. A second covering or pellicle gradu|ally forms above the first. Abundance of nou|rishment is furnished by the menstrual blood, which coagulates by degrees, and is converted into flesh. This flesh gradually articulates as it grows; and the spirit bestows this form upon it. Every part proceeds to take its proper place; the solid particles unite together; the moist particles associate by themselves; every thing searches for what is analogous to it; and, in fine, the foetus, by these causes and means, is completely formed.

This system is more rational, and less obscure than that of Aristotle; because Hippocrates en|deavours to explain every particular appearance, and borrows only one general principle from the philosophy of his times, namely, that heat and cold produce spirits, and that these spirits have the power of arranging and of bestowing

figure upon matter. He treats his subject more like a physician than a philosopher; but Aristotle explains the phaenomena of generation more as a metaphysician than a naturalist. It is for this reason that the errors of Hippocrates are parti|cular and less apparent, and that those of Aris|totle are general and evident.

These two great men have each had their fol|lowers. Almost all the philosophers of the schools adopted Aristotle's theory of generation, while most physicians adhered to the theory of Hippocrates; and, in this manner, 17 or 18 cen|turies passed without the appearance of any thing new upon this mysterious subject.

At last, upon the revival of literature, some a|natomists began to investigate the nature of gene|ration; and Fabricius ab Aquapendente was the first who thought of making a course of experi|ments upon the impregnation and expansion of the eggs of fowls, the substance of which we shall lay before the reader.

He distinguishes the matrix of a hen into two parts, the one superior, and the other infe|rior. The superior part, which he calls the ovarium, is an assemblage of a great number of small yellow eggs, of a round figure, the sizes of which vary from that of a mustard seed to that of a walnut. These eggs are attached to one another by foot-stalks, and the whole some|what resembles a bunch of grapes. The smallest

eggs are white, and they turn yellower in pro|portion as they increase.

Having examined those yellow eggs imme|diately after a communication with the male, he could perceive no sensible difference; he saw none of the male semen in any part of the eggs: He therefore concluded, that the whole eggs, and even the ovarium itself, were rendered fer|tile by a subtile spirit which issues from the male semen; and, he adds, that, in order to prevent the escape of this fecundating spirit, nature has placed, at the external orifice of the vagina of birds, a membranous valve which permits the seminal spirit to enter freely into the vagina, but prevents its return.

When an egg is detached from the common pedicle, it gradually descends, through a wind|ing canal, into the inferior part of the matrix. This canal is filled with a liquor very similar to the white of an egg. It is here that the egg receives its white liquor, the membrane in which it is inclosed, the two cords (chalazae) that run through the white, and join it to the yolk, and the shell which is suddenly formed immediately before exclusion. These cords, according to our author, are the part of the egg which is im|pregnated by the seminal spirit of the male; and it is here also that the rudiments of the foetus first appear. The egg is not only the true ma|trix, or the place where the chick is formed, but the whole business of generation depends upon

it. The egg is the great agent in generation; it furnishes both the matter and the organs. The substance of the cords is the matter of which the chick is formed; the white and the yok afford it nourishment; and the seminal spi|rit of the male is the efficient cause. This spirit communicates to the cords, first, an alterant quality, then a forming quality, and, lastly, a power of augmenting, &c.

These observations of Fabricius, it is apparent, lead not to any clear idea of generation. At the same time that this anatomist was making his experiments, which was about the middle of the sixteenth century, the famous Aldrovandus* 1.16 made some remarks upon eggs. But, as Har|vey properly observes of him, he followed more the authority of Aristotle than of experiment. The description he gives of the chick in the egg is by no means exact. Volcher Coiter, one of his pupils, succeeded better than his master; this writer, together with Parisanus, a Venetian phy|sician, have each given descriptions of the chick in the egg, which Harvey prefers to all the o|thers.

This celebrated anatomist, who first discover|ed the circulation of the blood, has given an ex|cellent treatise on generation. He flourished about the middle of last century, and was phy|sician to Charles I. of England. As he was o|bliged to follow this unhappy Prince during his

misfortunes, he lost, among other papers, what he had written concerning the generation of in|sects; and it appears, that he composed from memory his treatise on the generation of birds and of quadrupeds. I shall give a short view of his remarks, of his experiments, and of his the|ory.

Harvey alledges, that men, and all other ani|mals, proceed from eggs; that, in viviparous a|nimals, the first produce of conception is a kind of egg; and that the only difference between the viviparous and oviparous is, that, in the for|mer, the foetuses begin to exist, increase, and acquire their full growth in the uterus; but that, in the oviparous animals, the foetuses begin to exist in the body of the mother, where they are in the form of eggs; and it is only after their exclusion that they become real foetuses. And it deserves to be remarked, says he, that, in ovi|parous animals, some retain their eggs till they be perfect, as birds, serpents, and oviparous qua|drupeds; and that others exclude their eggs be|fore they are perfect, as fishes, crustaceous, and testaceous animals. The eggs laid by those crea|tures are only the rudiments of eggs, which af|terwards acquire membranes and a white, and attract nourishment from the matter with which they are surrounded. There are even, he adds, insects, caterpillars, for example, which are only imperfect eggs; they search for their nourish|ment, and, at the end of a certain time, they ar|rive

at the state of a chrysalis, which is a perfect egg. Another difference may still be remarked in oviparous animals: The eggs of hens, and other birds, are of all different sizes; but those of fishes, frogs, &c. who lay them before they are perfect, are all of the same size. He indeed observes, that, in pigeons, who lay two eggs, all the small eggs that remain in the ovarium are of the same bulk; and that the two only which are next to be excluded exceed the size of the rest. The same thing happens in cartilaginous fishes, as in the ray, which only brings to maturity two eggs at a time, all the rest being of different sizes, like those of the hen.

He next describes anatomically the parts ne|cessary to generation; and remarks, that the si|tuation of the anus and vulva in birds differ from those of all other animals, the anus being placed before, and the vulva behind* 1.17. And, with regard to the cock, and all small birds, he al|ledges, that they have no proper penis, and that they generate by rubbing, without any intro|mission. But male-ducks, geese, and ostriches, are amply provided with this instrument.

Hens produce eggs without the intervention of the cock; but, though perfect, they are fewer in number, and unfertile. He credits not the common opinion, that a few days inter|course with the cock are sufficient to impregnate all the eggs which a hen will lay during the year;

but he acknowledges, that he separated a hen from the cock for 20 days, and that all the eggs she laid were fecundated. As long as the egg remains attached to the ovarium, it is nourished by the vessels of the common pedicle; but, when it separates from this pedicle, it receives the white liquor and the shell from the matter with which the canal of the uterus is filled.

The two cords (chalazae) which Aquapen|dente considered to be the germ, or part produ|ced by the male semen, are found in unimpreg|nated, as well as impregnated eggs; and Harvey properly observes, that these parts neither pro|ceed from the male, nor receive the impregna|tion. The part of the egg which receives the impregnation is a small white circle situated up|on the membrane that covers the yolk, and has the appearance of a cicatrice about the size of a lentil. Harvey likewise remarks, that this ci|catrice is found in all eggs, whether they be fe|cundated or not; and that those are deceived who imagine it to be produced by the seed of the male. It is of the same size and form in fresh eggs as in those which have been long kept. But, as soon as the process of hatching is begun, whether by means of artificial heat, or by the heat of the hen, this small mark or cicatrice gradual|ly augments and dilates like the pupil of the eye. This is the first change, and it is visible after a few hours incubation.

When the egg has been heated for 24 hours, the yolk, which was formerly in the centre, rises 〈…〉〈…〉 the cavity at the thick end of the egg This cavity continues to enlarge by the 〈…〉〈…〉 of the more fluid part of the white; and the heaviest part of the white falls down to the small end. The cicatrice or speck on the membrane of the yolk, is elevated along with it, and applies itself to the membrane which lines the cavity at the thick end. This speck is now as large as a pea; and a white point is distinguishable in the middle of it, with several circles, of which this point appears to be the common centre.

At the end of the second day, these circles are larger and more conspicuous, and they divide the speck sometimes into two, and sometimes into three parts, of different colours. A small external pro|tuberance likewise appears, which nearly resem|bles a little eye, with a white point or cataract on the pupil. Between the circles a liquor, as transparent as crystal, is contained by means of a very thin membrane. The speck, which is now become a kind of bubble, or liquid globe, appears as if it were situated in the white, rather than on the membrane of the yolk. On the third day the transparent liquor, as well as the mem|brane in which it is inclosed, is considerably aug|mented. On the 4th, a small line of blood, of a purple colour, appears on the circumference of the bubble; and, at a little distance from the

centre, we perceive a dot or point, of a bloody colour, which beats like a heart. It is visible at every diastole, and disappears during the systole. From this animated point two small blood-vessels issue, and terminate in the membrane which con|tains the transparent crystalline liquor. These blood-vessels set off from the same place, nearly in the same manner as the roots of a tree set off from the trunk; and it is in the angle which these roots form with the trunk, and in the mid|dle of the liquor, that the animated point is si|tuated.

Towards the end of the fourth, or beginning of the fifth day, the animated point is so much enlarged, that it has the appearance of a small bladder filled with blood; and, by its contractions and dilatations, it is alternately filled and emp|tied. On the same day we distinctly perceive, that this bladder is divided into two parts, each of which dilates and contracts in the same manner. Round the shortest of the blood-vessels described above, a kind of cloud appears, which, though transparent, obscures the view of the vessel. E|very hour this cloud becomes thicker; it attach|es itself to the root of the blood-vessel, and seems to depend from it like a small globe. This globe extends and appears to divide into three parts, one of which is globular, and larger than the o|ther two; and here we perceive the rudiments of two eyes, and of the whole head: And, at the end of the fifth day, we see, in the remain|der of this lengthened globe, the beginnings of the vertebrae.

On the sixth day, the parts of the head are more apparent. We distinguish the coats of the eyes, the thighs, and wings; and then the liver, the lungs, and the beak. The foetus now begins to move and to stretch out its head, though no|thing but the viscera are yet formed; for the thorax, the abdomen, and all the external co|verings of the fore part of the body, are still wanting. At the end of this day, or the begin|ning of the seventh, the claws begin to be vi|sible; the chick opens and moves its beak; and the anterior parts of the body begin to cover the viscera. On the seventh day, the chick is en|tirely formed; and, from this time till it issues from the egg, nothing happens but an expansion of all the parts it acquired during the first seven days. The feathers appear on the 14th or 15th day; and, on the 21st, it escapes from the egg, by breaking the shell with its bill.

These experiments of Harvey appear to have been made with the greatest exactness and fide|lity. In the sequel, however, we shall demon|strate their imperfection, and that the author has probably fallen into the common error of ma|king experiments, with a view to establish his fa|vourite hypothesis, that the first animated point which appeared was the heart. But, before pro|ceeding to this object, it is proper to give an ac|count of his other experiments.

Every body knows the many experiments of Harvey made upon female deer. They receive

the male about the middle of September. A few days after copulation, the horns* 1.18 of the ute|rus appear to be thicker and more fleshy than usual: They are, at the same time, more lax and flabby; and, in each of their cavities, five ca|runculae, or soft warts, appear. About the 26th or 28th of September, the uterus is still thicker; the five carunculae are swelled nearly to the size and form of a nurse's nipple. On opening them with a scalpel, they appeared to be filled with an infinite number of white points. Harvey pre|tends to have remarked, that, neither now, nor immediately after copulation, had the ovarium suffered any change; and that he never could discover, after repeated trials, the least drop of male semen in the uterus.

Towards the end of October, or the beginning of November, when the females were separated from the males, the thickness of the horns began to diminish; the internal surfaces of their cavi|ties were swelled, and seemed to be glued toge|ther. The carunculae still remained; and the whole resembled the substance of the brain, be|ing so soft that it could not be touched. Har|vey tells us, that on the 13th or 14th of Novem|ber, he perceived filaments, like those of a spi|der's web, which traversed the cavities of the horns, and even that of the uterus itself. These filaments arose from the superior angle of the

horns, and, by their number, formed a kind of membrane or empty coat. A day or two after|wards, this coat or sac was filled with a white, aqueous, viscid matter, and adhered to the ute|rus by means of a species of mucilage; and the adhesion was most sensible at the superior part of the uterus, where the rudiments of the placenta began then to appear. In the third month, this sac contained an embryo of two fingers breadth in length, and also an internal sac, called the amnios, inclosing a transparent crystalline liquor, in which the foetus swam. The foetus, at first, was only an animated point, like what ap|peared in the hen's egg. Every thing now pro|ceeded and terminated in the same manner as described with regard to the chick, with this on|ly difference, that the eyes of the chick appear|ed much sooner than those of the deer. The a|nimated point was visible about the 19th or 20th of November. A day or two afterwards, the oblong body, which contained the rudiments of the foetus, made its appearance. In six or seven days more, the foetus was so compleatly formed, that all its members, and even its sex, were di|stinguishable. But the heart and viscera were still bare; and it was not till a day or two after, that they were covered with the abdomen and thorax. This is the last work, the slating of the edifice.

From these experiments upon hens and deer, Harvey concludes, that all female animals have

eggs; that in these eggs a separation of a transpa|rent crystalline liquor, contained in a sac (amnios), takes place, and that another external sac (chorion) incloses the whole liquors of the egg; that the first thing which appears in the crystalline li|quor is an animated sanguineous point; and, fi|nally, that the formation of viviparous animals is effected in the same manner with that of the oviparous: The following is the account which he gives of the generation of both.

Generation, he observes, is an operation of the uterus alone; for not a drop of the male semen ever enters it. The uterus conceives by a kind of contagion, communicated to it by the semen of the male, nearly in the same manner as the load-stone communicates a magnetic virtue to iron. This male contagion acts not only on the uterus, but on the whole body of the female, which is entirely fecundated, though the uterus alone possesses the faculty of conception, in the same manner as the brain has the sole power of conceiving ideas. The ideas conceived by the brain are similar to the images of the objects transmitted to it by the senses; and the foetus, which may be regarded as the idea of the uterus, is similar to that which produces it. This is the reason why children resemble their fathers, &c.

I will follow the system of our anatomist no farther: What has been said is sufficient to en|able the reader to judge of it. But we have re|marks of importance to make concerning his

experiments. He has represented them in a manner the most plausible and insinuating. He appears to have often repeated them, and to have taken every necessary precaution to avoid fallacy and deception; and, of course, we are led to think that he has seen every thing which possi|bly could be discovered. Uncertainty and ob|scurity, however, are perceptible in his descrip|tions. His observations are related from memo|ry; and he seems, though he often maintains the contrary, to have made Aristotle, more than experience, his guide; for he has seen every thing in eggs, and very little more, than was mentioned by that philosopher. That the most material of his observations were made long be|fore his own time, we shall be convinced by at|tending to what follows.

Aristotle knew, that the cords (chalazae) in eggs were of no use in the generation of the chick: 'Quae ad principium lutei grandines haerent, nil conferunt ad generationem, ut qui|dam suspicantur* 1.19.' Parisanus, Volcher Coiter, Aquapendente, &c. had remarked the small ci|catrice, as well as Harvey. Aquapendente be|lieved it to be of no use; but Parisanus main|tained that it was formed by the male semen, or, at least, that the white point in the middle of the cicatrice was the semen of the male, and that it was the rudiments of the foetus, 'Estque,' says he, 'illud galli semen alba et tenuissima tu|nica

abductum, quod substat duabus communi|bus toti ovo membranis,' &c. Hence the only discovery proper to Harvey is his having re|marked the existence of this cicatrice, both in fecundated and unfecundated eggs; for the o|ther writers had observed, as well as he, the di|latation of the circles, and the growth of the white point. These are all the remarks Harvey has made in his account of the two first days of incubation; what he mentions concerning the third day is only a repetition of what Aristotle delivers in the sixth book and fourth chapter of his history of animals: 'Per id tempus ascendit jam vitellus ad superiorem partem ovi acutio|rem, ubi et principium ovi est et foetus exclu|ditur; corque ipsum apparet in albumine san|guinei puncti, quod punctum salit et movet se|se instar quasi animatum; ab eo meatus vena|rum specie duo, sanguine pleni, flexuosi, qui, crescente foetu, feruntur in utramque tunicam ambientem, ac membrana sanguineas fibras ha|bens eo tempore albumen continet sub meati|bus illis venarum similibus; ac paulo post dis|cernitur corpus pusillum initio, omnino et can|didum, capite conspicuo, atque in eo oculis maxime turgidis qui diu sic permanent, sero e|nim parvi siunt ac considunt. In parte autem corporis inferiore nullum extat membrum per initia, quod respondeat superioribus. Meatus autem illi qui a corde prodeunt, alter ad cir|cumdantem

cumdantem membranam tendit, alter ad lute|um, officio umbilici.'

Harvey, because Aristotle says that the yolk rises to the small end of the egg, concludes that he had seen nothing himself, but had received his information from some other pretty accurate observer. In this accusation, Harvey evidently injures Aristotle; for the rising of the yolk to either end, solely depends upon its position du|ring the time of incubation; for the yolk, being lighter than the white, uniformly mounts to the top, whether the large or the small end of the egg be uppermost. This observation we owe to William Langley, a physician in Dordrecht, who made experiments on the hatching of eggs in the year 1655, about 20 years before Harvey's time* 1.20.

But, to return to the passage we have quoted. It is apparent, that the crystalline liquor, the animated point, the two circles, the two blood-vessels, &c. are described by Aristotle in the same manner as they were seen by Harvey. This anatomist maintains, that the animated point is the heart, that the heart is the first part of the foetus which is formed, and that the viscera and other members succeed. All this has been men|tioned by Aristotle, and seen by Harvey; and yet it is by no means consonant to truth. To be assured of this fact, we have only to repeat the same experiments, or to read with attention those

of Malpighius* 1.21, which were made about 50 years after the trials of Harvey.

Malpighius carefully examined the cicatrice, which is the essential part of the egg; he found that it was large in impregnated eggs, and small in those which had received no impregnation; and he discovered, that, in eggs which had ne|ver been sit upon, the white point, mentioned by Harvey as the first part that becomes animated, is a small purse or bubble swimming in the li|quor bounded by the first circle; and that the embryo is visible in the centre of this purse. The membrane of the purse, which is the am|nios, being exceedingly thin and transparent, allowed him to see distinctly the foetus within it. Malpighius, from this first observation, con|cludes with propriety, that the foetus exists in the egg before incubation, and that the rudi|ments of the embryo are even then deeply rooted. It is unnecessary to mention how much this ex|periment differs from the opinion of Harvey; for he had observed nothing begun to be formed during the two first days of incubation; and, in his estimation, the first vestige of a foetus is the animated point, which appears not till the third day. But Malpighius discovered that the rudi|ments of the whole foetus exist before incuba|tion is commenced.

After ascertaining this important fact, Mal|pighius proceeded to examine the cicatrice of unimpregnated eggs, which, as formerly re|marked,

is smaller than in those that have received an impregnation. Its margin is often irregular, and its texture sometimes differs in different eggs. Near its centre, in place of a bubble including the foetus, there is a globular mole or unorgani|zed mass, which, when opened, presents nothing like regularity or arrangement of parts: It has only some appendages filled with a thick but transparent liquor; and this unformed mass is surrounded and enveloped in several concentric circles.

After six hours incubation, the cicatrice is con|siderably enlarged; and, in its centre, a bubble or globule formed by the amnios is easily di|stinguishable. This globule is filled with a fluid, in the middle of which the head and back-bone of the chick visibly appear. Six hours after this, every thing is enlarged, and, of course, more apparent to the eye. In six hours more, that is, 18 hours after the commencement of in|cubation, the head is larger, and the spine is lengthened; and, at the end of 24 hours, the head of the chick appears in a bended posture, and the spine is of a whitish colour. The ver|tebrae are ranged on each side of the spine, like small globules; and, nearly at the same time, the wings begin to sprout, and the head, neck, and breast, are lengthened. At the end of 30 hours, nothing new appears; but all the parts are enlarged, and especially the amnios. Round this membrane, may be remarked the umbilical

vessels, which are of a dark colour. In 38 hours, the chick has acquired more strength; its head is very large, and three vesicles appear in it sur|rounded with membranes, which likewise in|clude the spine of the back, through which, however, the vertebrae are still visible. At the end of 40 hours, it was admirable to observe, continues our author, the chick living in the centre of the liquor of the amnios. The back-bone was increased, the head was bended, the vesicles of the brain were less bare, the rudi|ments of the eyes appeared, the heart beat, and the blood circulated. Here Malpighius describes vessels and the circulation of the blood; and he thought, with reason, that, though the heart did not beat till 38 or 40 hours after incubation was begun, it nevertheless existed before, as well as the other parts of the chick. But, on exami|ning the heart in a dark chamber, he observed nothing like luminous sparks issuing from it, as Harvey seems to insinuate.

At the end of the second day, the foetus ap|peared swimming in the liquor of the amnios; the head, which seemed to be composed of ve|sicles, was bended; the back-bone and verte|brae were lengthened; the heart, which hung out of the breast, beat three times successively, because the fluid it contains is pushed from the auricle into the ventricles, from the ventricles into the arteries, and, lastly, into the umbilical vessels. He remarks, that, having separated the

chick from the white of the egg, the motion of the heart continued for a whole day. In 14 hours more, or 62 hours from the beginning of the incubation, the chick, though stronger, re|mained still with its head bended in the liquor of the amnios: Veins and arteries were perceived among the vessels of the brain; and the linea|ments of the eyes, and of the spinal marrow, ap|peared. At the end of three days, the body of the chick was crooked. Beside the two eyes, five vesicles filled with liquor appeared in the head; the rudiments of the thighs and of the wings were discernible; the body began to take on flesh; and the pupils of the eyes, and likewise the crystalline and vitreous humours, were dis|tinguishable. At the termination of the fourth day, the vesicles of the brain were nearer each other; the processes of the vertebrae were long|er; the wings and the thighs had become strong|er, in proportion as they grew longer; the whole body was covered with an unctuous flesh; the umbilical vessels had pierced through the abdo|men; and the heart was concealed within the breast, which was now shut up by a thin mem|brane. On the fifth, and at the end of the sixth day, the vesicles of the brain began to be covered; the spinal marrow, which was now more solid, was divided into two parts, and advanced along the trunk; the thighs and wings were longer, and the wings were unfolded; the abdomen was shut and tumified; the liver was distinctly visible,

and of a dark colour; the two ventricles of the heart beat; the body of the chick was covered with skin; and the points of the feathers began to appear. On the seventh day, the head was very large; the brain was covered with its mem|branes; the beak appeared between the two eyes; the wings, the thighs, and the legs, had acquired their perfect form; the heart seemed to be composed of two ventricles, like two con|tiguous globules, united at their superior part with the auricles; and two successive pulses were remarked both in the ventricles and auricles, as if there had been two separate hearts.

But I will follow Malpighius no farther. The remainder of the detail regards the growth and perfection of the parts till the chick breaks the shell in which it is inclosed, and becomes an in|habitant of a new world. The heart is the last part that assumes its proper figure, by the union of its ventricles, which happens not till the e|leventh day.

We are now in a condition to form a distinct judgment concerning the value of Harvey's ex|periments. It is probable that this celebrated anatomist did not make use of the microscope, (which was, indeed, very imperfectly known in his days), otherwise he never would have affirm|ed, that there was no difference between the cicatrice of impregnated and unimpregnated eggs; he never would have said, that the semen of the male produced no change upon the egg,

and particularly upon the cicatrice; he never would have advanced, that nothing was percep|tible before the end of the third day; that the animated point appeared first; and that the white point was transformed into the animated point: He would have perceived that the white point was the bubble or globule which contained the whole apparatus of generation; and that all the rudiments of the foetus commenced there from the moment of receiving the impregnation of the cock: He would likewise have discovered, that, without this impregnation, it contains no|thing but an unformed mass, which could never become animated; because, in fact, it is not organized like an animal, and because it is only after this mass, which ought to be regarded as a collection of the organic particles of the female semen, is penetrated by the organic particles of the male semen, that an animal is formed. This formation is instantaneous; but the motions of the new animal are imperceptible till 40 hours after the process of incubation has commenced: He would not have assured us, that the heart is first formed, and that the other parts are succes|sively joined to it by juxta-position; since it is apparent, from the experiments of Malpighius, that the rudiments of all the parts are formed at once, but that they become perceptible only in proportion as they are successively unfolded: Lastly, if he had seen, as Malpighius saw, he would not have positively asserted, that no im|pression

of the male seed remained in the eggs, and that it was only by contagion that they were impregnated, &c.

It is also proper to remark, that what Harvey has said concerning the parts of generation of the cock is by no means exact. He affirms, that the cock has no penis capable of entering the vagina of the hen. It is certain, however, that this animal, in place of one penis, has a couple, which both act at the same time; and this action is a vigorous compression, if not an actual copulation* 1.22. It is by this double organ that the cock throws his seminal liquor into the uterus of the hen.

Let us now compare Harvey's experiments upon female deer with those of de Graaf upon female rabbits; and, though de Graaf believed, as Harvey did, that all animals proceed from eggs, we shall find a very great difference in the manner in which these two anatomists have per|ceived the first formation, or rather the expan|sion, of the foetuses of viviparous animals.

After exerting every effort to prove, by ar|guments drawn from comparative anatomy, that the testicles of viviparous females are true ova|ria, Graaf explains the manner in which the eggs are detached from the ovaria, and fall into the horns of the uterus; and then he relates the remarks he made upon a rabbit which he dis|sected half an hour after copulation. The horns

of the uterus, he says, were uncommonly red; there was no change either in the ovaria, or in the eggs which they contained; and there was not the least appearance of semen in the vagina, in the uterus, or in the Fallopian tubes.

Having dissected another rabbit, six hours af|ter copulation, he observed, that the follicles, or coats, which, in his estimation, contain the eggs in the ovarium, were become red; but he found no male semen either in the ovaria or any where else. Twenty hours after copulation, he dissect|ed a third; he remarked in one ovarium three, and in the other five follicles much altered; for instead of being clear and limpid, they were become opaque and reddish. In another, dis|sected twenty-seven hours after copulation, the horns of the uterus, and the superior canals which terminate in them, were still more red, and their extremities embraced the ovarium on all sides. In another, which was opened forty hours after copulation, he found in one ovarium seven, and in the other three follicles changed. Fifty-two hours after copulation, he examined another, and found in one ovarium four changed follicles, and one in the other; and having open|ed these follicles, he discovered in them a kind of glandular liquor, with a small cavity in the middle, where he could perceive no fluid, which made him suspect that the transparent liquor usually contained in the follicles, and which, he says, is inclosed in its own membranes, might

have been discharged by some kind of rupture. He searched for this matter in the canals which terminate in the horns of the uterus, and in the horns themselves; but he found nothing. He only remarked, that the membranes which line the horns of the uterus were much swelled. In another rabbit, dissected three days after copu|lation, he observed, that the superior extremity of the canal, which terminates in the horns of the uterus, straitly embraced the ovarium on every side: And, having separated it from the ovarium, he remarked, in the right ovarium, three follicles somewhat larger and harder than usual. After searching with great care the ca|nals above mentioned, he discovered, he says, an egg in the right canal, and two more in the right horn of the uterus, so small that they ex|ceeded not mustard seeds. These little eggs had each two membranes, and the internal one was filled with a very limpid liquor. Having examined the other ovarium, he found four changed follicles; three of them were whiter, and had likewise some limpid liquor in their centres; but the fourth was of a darker colour, and contained no liquor, which made him sus|pect that the egg had escaped from it. He there|fore searched the corresponding canal and horn of the uterus; he found an egg in the superior extremity of the horn, which was exactly simi|lar to those he had discovered in the right horn. He alledges, that the eggs, when they are sepa|rated

from the ovarium, are ten times less than before their separation; and this difference in size, he imagines, is owing to the eggs, while in the ovarium, containing another matter, namely, the glandulous liquor which he remarked in the follicles.

Four days after copulation, he opened another rabbit, and he found in one ovarium four, and in the other three follicles void of eggs: In the horns corresponding to the ovaria, he found four eggs on one side, and three in the other. These eggs were larger than those he had discovered three days after copulation. They were nearly of the size of the lead-shot used for shooting small birds; and he remarked, that, in these eggs, the interior membrane was separated from the exterior, and appeared as if a second egg was contained within the first. In another, dis|sected five days after copulation, he found five empty follicles in the ovaria, and an equal num|ber of eggs in the uterus, to which they adhe|red very firmly. These eggs were as large as the shot employed for killing hares, and the in|ternal membrane was still more apparent than in the last experiment. Having opened another rabbit, six days after copulation, he found in one of the ovaria six empty follicles, but only five eggs in the corresponding horn of the ute|rus, and they seemed to be all accumulated into one mass: In the other ovarium, he saw four empty follicles, and found but one egg in the

corresponding horn. These eggs were of the size of the largest fowling shot. Seven days af|ter copulation, our anatomist opened another rabbit, and he found in the ovaria some empty follicles, which were larger, harder, and more red than those he had formerly observed; and he perceived as many transparent tumors in dif|ferent parts of the uterus; and, having opened them, he took out the eggs, which were as large as small pistol bullets. The internal membrane was more distinct than formerly; and within this membrane he saw nothing but a very clear li|quor. In another, dissected eight days after co|pulation, he found in the uterus the tumors or cells which contain the egg; but they adhered so strongly to the uterus, that he could not de|tach them. In another, which he opened nine days after copulation, he found the cells con|taining the eggs greatly enlarged, and he per|ceived in the middle of the liquor inclosed by the internal membrane a small thin cloud. In another, which he opened ten days after copu|lation, the small cloud was thicker and darker, and formed an oblong body like a little worm. Lastly, twelve days after copulation, he distinctly perceived the embryo, which, though two days before, it was only an oblong body, was now so apparent, that he could distinguish its different members. In the region of the breast, he saw two red and two white points, and, in the ab|domen, a mucilaginous reddish substance. Four|teen

days after copulation, the head of the foe|tus was large and transparent; the eyes were prominent; the mouth was open; the rudi|ments of the ears appeared; the back-bone was whitish, and bended towards the sternum, and small blood-vessels arose from each side of it, the ramifications of which extended along the back as far as the legs: The two red points were considerably enlarged, and appeared like the rudiments of the ventricles of the heart; on each side of the red points he saw two white ones, which were the rudiments of the lungs. In the abdomen he saw the rudiments of the li|ver, which was reddish, and a small body twisted like a thread, which was the stomach and inte|stines. After this, till the 31st day, when the female rabbit brings forth, there was nothing to be remarked but the gradual expansion and growth of the parts which were already formed.

From these experiments, De Graaf concludes, that all viviparous females have eggs; that these eggs are contained in the ovaria or testicles; that they cannot be separated till they are fecun|dated by the semen of the male; because, says he, the glandular liquor, by means of which the eggs are enabled to escape from their follicles, is not secreted till after an impregnation by the male. He alledges, that those who imagine they have seen pretty large eggs in three days, have been deceived; because, in his opinion, the eggs, though fecundated, remain longer in the ovarium, and,

in place of augmenting, they become ten times less than formerly, and they never begin to grow till after their descent from the ovaria in|to the uterus.

By comparing these observations of Graaf with those of Harvey, we will easily perceive that the latter has missed the principal facts: And, though there are several errors both in the reasoning and in the experiments of De Graaf, this anatomist, as well as Malpighius, have dis|covered themselves to be better observers than Harvey. They agree in all fundamental points, and both of them contradict Harvey. He per|ceived not the alterations which take place in the ovaria; he saw not in the uterus those small globules which contain the materials of genera|tion, and which are called eggs by De Graaf; he never suspected that the foetus existed in this egg; and, though his experiments give us tole|rably exact ideas concerning what happens du|ring the growth of the foetus, he furnishes no information concerning the commencement of fecundation, nor concerning the first expansion of the foetus. Schrader, a Dutch physician, who had a great veneration for Harvey, acknow|ledges that he cannot be trusted in many articles, and particularly in what relates to the first for|mation of the embryo; for the chick really ex|ists in the egg before incubation; and, he says, that Joseph of Aromatarius was the first who

made this material observation* 1.23. Besides, though Harvey alledged that all animals proceeded from eggs, he never imagined that the testicles of fe|males contained eggs; and it was only from a comparison between the sac, which he believed to be formed in the uterus of viviparous ani|mals, with the growth and covering of the eggs in oviparous animals, that he maintained that all animals were produced from eggs; and even this is only a repetition of what Aristotle had said before him. Steno was the first who pre|tended to have discovered eggs in the ovaria of females. He says, that, in dissecting a female sea-dog, he perceived eggs in the testicles, though this animal be viviparous; and he adds, that the testicles of women are analogous to the ovaria of oviparous animals, whether the eggs them|selves fall into the uterus, or only the matter which they contain. Steno was the first who discovered these supposed eggs; De Graaf is willing to assume the discovery to himself; and Swammerdam warmly disputes the point with him, and alledges that Van-Horn had seen them before De Graaf. This last writer, it is true, has been accused of asserting many things which have been contradicted by experiments: He even pretended, that a certain judgment might be formed of the number of foetuses in the ute|rus, by the number of cicatrices or empty fol|licles in the ovaria. In this he is contradicted

by the experiments of Verrheyen* 1.24, by those of M. Mery* 1.25, and by some of his own, where he found fewer eggs in the uterus, than cicatrices in the ovaria. Besides, we shall demonstrate that what he says concerning the separation of the eggs, and the manner in which they descend into the uterus, is by no means exact; that no eggs exist in the testicles of females; that what is seen in the uterus is not an egg; and that the systems which have been deduced from the ob|servations of this celebrated anatomist are per|fectly chimerical.

This pretended discovery of eggs in the testi|cles of females attracted the attention of most anatomists. They only found, however, in the testicles of viviparous females, small bladders; those they hesitated not to consider as real eggs, and, therefore, they called the testicles ovaria, and the vesicles eggs. They asserted also, like De Graaf, that these eggs differed in size in the same ovarium; that the largest in the ovaria of women exceeded not the bulk of a small pea; that they are very small in young girls; but that they increased with age and intercourse with men; that not above 20 could be reckoned in each ovarium; that these eggs are fecundated in the ovarium by the spirituous part of the male semen; that they then separate and fall into the uterus by the Fallopian tubes, where the

foetus is formed of the internal substance of the egg, and the placenta of its external part; that the glandulous matter, which exists not in the ovarium till after a fruitful embrace, compresses the egg, and excludes it from the ovarium, &c. But, though Malpighius, who examined mat|ters more accurately, detected many errors com|mitted by those anatomists even before they were received; yet most physicians adopted the o|pinion of De Graaf, without regarding the ob|servations of Malpighius, which were neverthe|less of the greatest importance, and which re|ceived much weight from the experiments of his disciple Valisnieri.

Malpighius and Valisnieri, of all naturalists, appear to have written with most judgment and acuteness on the subject of generation. We shall, therefore, give an account of their experi|ments and remarks.

Malpighius, having examined the testicles of a number of cows and other female animals, assures us, that he found, in the testicles of all of them, vesicles of different sizes, whether the females were very young or adults. These ve|sicles are enveloped in a pretty thick membrane, the inside of which is interspersed with blood-vessels; and they are filled with a kind of lymph or liquor, which coagulates and hardens by the heat of a fire, like the white of an egg.

In process of time, a firm yellow body ad|heres to the testicles. It is prominent, and in|creases

to the size of a cherry, and occupies the greatest part of the ovarium. This body con|sists of several angular lobes, the position of which is very irregular, and it is covered with a coat or membrane interspersed with nerves and blood-vessels. The form and appearance of this yellow body varies considerably at different times. When it exceeds not the size of a grain of millet, it is roundish, and its substance, when cut, has a warty appearance. We often find an external covering round the vesicles of the o|varia, which consists of the same substance with the yellow bodies.

When the yellow body has become nearly of the size of a pea, it resembles a pear; and, in the centre of it, there is a small cavity filled with liquor. The same thing may be remarked when it is as large as a cherry. In some of these yellow bodies, after they have arrived at full maturity, Malpighius affirms that he saw, to|wards the centre, a small egg with its appen|dages, about the size of a millet seed; and, after they had discharged these eggs, they were flaccid and empty. They then resembled a cavernous canal; and the void cavities were as large as peas. He conceived that Nature designed this yellow glandular body for the preservation of the egg, and for making it escape from the te|sticles; and that, perhaps, it contributed to the formation of the egg; consequently, he remarks, the vesicles which are at all times found in the

ovarium, and always differ in size, are not the true eggs which receive the impregnation, but only serve to produce the yellow bodies in which the eggs are formed. Besides, though these yel|low bodies are not always found in every ova|rium; yet we always find the rudiments of them. Malpighius found the marks of them in new born heifers, in cows with calf, and in preg|nant women; and, therefore, he properly con|cludes, that these yellow glandular bodies are not, as De Graaf asserts, an effect of impregna|tion. The yellow bodies, he remarks, produce unfecundated eggs, which fall out of the ova|rium independent of any communication with the male, and also those which fall after impreg|nation. When the impregnated eggs fall into the uterus, every thing proceeds in the manner described by De Graaf.

These observations of Malpighius demonstrate, that the testicles of females are not real ovaria; that the vesicles they contain are not eggs; that these vesicles never fall into the uterus; and that the testicles, like those of males, are only reser|voirs containing a liquor which may be regarded as female semen in an imperfect state. This se|men is matured in the yellow glandular bodies, of which it fills the internal cavities, and flows out after the yellow bodies have acquired their full size.

But, before we form a judgment concerning this important point, we must attend to the re|marks of Valisnieri.

In the year 1692, Valisnieri began his expe|riments upon the testicles of the sow. The te|sticles of the sow differ from those of cows, of mares, of sheep, of she-asses, of female-dogs, of she-goats, of women, and of most viviparous animals; for they resemble a small bunch of raisins, the grains of which are round and pro|minent on the outside; between these grains are smaller ones, not yet arrived at maturity. These grains appear not to be covered with a common membrane. They are, says he, analogous to the yellow bodies observed in cows by Malpi|ghius; they are round, and of a reddish colour; their surface is interspersed with blood-vessels, like the eggs of viviparous animals; and the whole grains together form a mass that is larger than the ovarium. With a little address, these grains may be separated from the ovarium, and each of them, after separation, leaves a nitch or depression.

These glandular bodies are not of the same colour in every sow. In some they are more red; in others more clear; and they are of all sizes, from the smallest seed, to that of a raisin. On opening them, a triangular cavity appears, filed with a limpid liquor, which coagulates with heat, and becomes white, like that which is contained in the vesicles. Valisnieri expected to find the egg in some of these cavities: But in this he was disappointed; though he made a careful search into all the glandular bodies of a

number of sows, and other animals, he could never discover the egg, which Malpighius af|firms he found once or twice.

Under these glandular bodies, the vesicles of the ovarium appeared. They were more or less numerous, according as the glandular bodies were larger or smaller; for, in proportion to the largeness of the glandular bodies, the vesicles diminished. Some vesicles were of the size of a lentil, and others exceeded not that of a millet seed. In the testicles, when raw, from 20 to 35 vesicles might be reckoned; but, when boiled, a much greater number appear, and they are so firmly attached, that they cannot be separated without breaking some of them.

Having examined the testicles of a young sow, which had never brought forth, he found, as in the others, the glandular bodies; and their tri|angular cavities were likewise filled with lymph; but he could not discover any eggs either in the one or the other. The vesicles of this young sow were more numerous than in those which had brought forth, or those which were impregnated at the time of examination. In the testicles of another sow, which was far advanced in preg|nancy, Valisnieri found two of the largest glan|dular bodies, which were flaccid and empty, and others, of a lesser size, in their ordinary state; and, in several others which he dissected when with young, he remarked, that the number of glandular bodies was always greater than the

number of foetuses. This confirms what we observed concerning the experiments of De Graaf, and proves that they are by no means exact. What he calls follicles of the ovarium are only the glandular bodies, the number of which al|ways exceeds that of the foetuses. In the ova|ria of a sow, two or three months old, the tes|ticles were pretty large, and interspersed with vesicles of a considerable size. Among the ve|sicles, the beginnings of four glandular bodies appeared in one testicle, and of seven in the other.

After these experiments upon sows, Valisnieri repeats those of Malpighius upon cows, and he found them to be exactly conformable to truth. He indeed acknowledges, that he was never able to discover the egg which Malpighius ima|gined he had seen once or twice in the interior cavity of the glandular bodies. After a fruitless search in the testicles of so many different fe|males, it was natural to think, that Valisnieri would at least have doubted the existence of such eggs. But prejudice in favour of system made him admit, contrary to his own experience, the existence of eggs, which neither he nor any other man ever saw, or will see.

It is, perhaps, impossible to make a greater number, or more exact experiments, than Valis|nieri has done. Among other animals, he ex|amined the ewe, and found, that she has never any more glandular bodies in her testicles than

foetuses in the uterus. In young ewes, which were never impregnated, there is but one glan|dular body in each testicle, and, when one is emptied, it is succeeded by another; if a ewe has one foetus in the uterus, she has only one glandular body in her testicles; and if she has two foetuses, she has likewise two glandular bo|dies. This glandular body occupies the greatest part of the testicle; and, after it is emptied and disappears, another begins to grow for the pur|pose of a future generation.

In the testicles of a she-ass, he found vesicles as large as small cherries, which is an evident proof that they are not eggs, as it would be im|possible for them to pass, by the Fallopian tubes, into the uterus.

The testicles of female wolves, dogs, and foxes, are covered with a membrane, like a purse, which is an expansion of that which surrounds the horns of the uterus. In a bitch which began to be in season, but had not been approached by the male, Valisnieri found the internal part of this purse, which does not adhere to the testicle, moistened with a liquor that resembled whey, and two glandular bodies in the right testicle, about two lines in diameter, and which occu|pied nearly the whole extent of the testicle. Each glandular body had a small nipple, with a distinct fissure, from which, without pressing it, there issued a liquor like clear whey; he there|fore concluded, that this liquor was the same

which he found in the purse. He blew into this fissure with a pipe, and the whole glandular body immediatly swelled; and, having introdu|ced a bristle, he easily penetrated to the bottom of it. He opened the body on that side where he had introduced the bristle, and found an in|ternal cavity which communicated with the nipple, and contained a considerable quantity of liquor. Valisnieri was always in hopes of dis|covering the egg; but these hopes, notwithstand|ing all his researches, were uniformly frustrated. He likewise found, in the left testicle, two glan|dular bodies very similar to those in the right. He boiled two of these glandular bodies, hoping, that, by this means, he might discover the egg, but still without any measure of success.

Having dissected another bitch four or five days after she had received the male, he found in the testicles three glandular bodies exactly similar to the former. He searched every where for the egg; but he was still disappointed. By the assistance of the microscope, he discovered the glandular bodies to be a net-work composed of an infinite number of globular vesicles, which served to filtre the liquor which issued through the nipple.

He then opend another bitch which was not in season, and having tried to introduce air be|tween the testicle and the purse which covered it, he found that it dilated like a bladder filled with air. Having removed the purse, he disco|vered

two glandular bodies upon the testicles; but they had neither nipple nor fissure, and no liquor distilled from them.

In another bitch that had brought forth about five whelps two months before, he found five glandular bodies; but they were much diminish|ed in size, and they began to disappear without leaving any cicatrices; there remained only a small cavity in their centre; but it contained no liquor.

Not satisfied with these and many other ex|periments, Valisnieri, who passionately desired to discover this pretended egg, called together the best anatomists his country afforded, and, a|mong others, M. Morgagni; and, having open|ed a young bitch that was for the first time in season, and that had been covered three days be|fore, they examined the vesicles of the testicles, the glandular bodies with their nipples, their ca|nals, and the liquor in their internal cavities; but they could perceive no eggs. He then, with the same intention, made experiments on she-goats, foxes, cats, a number of mice, &c. In the testicles of all these animals, he uniformly found the vesicles, and frequently the glandular bodies with the liquor they contained; but no egg ever appeared.

In fine, being desirous of examining the te|sticles of women, he had an opportunity of o|pening a young country-woman, who had been some years married, and who was killed by a

fall from a tree. Though of a robust and vigo|rous constitution, she had never born any chil|dren. He endeavoured to discover if the cause of her barrenness existed in the testicles; and he found that the vesicles were all filled with a blackish and corrupted matter.

In a young girl of eighteen years of age, who had been brought up in a convent, and who had every appearance of real virginity, he found the right testicle a little longer than the left: It was of an oval figure, and its surface was somewhat unequal. This inequality was occasioned by five or six vesicles which protruded on the outside of the testicle. One of these vesicles, which was more prominent than the rest, he opened, and a quan|tity of lymph rushed out of it. This vesicle was surrounded with a glandular substance, in the shape of a crescent, and of a reddish yellow co|lour. He cut the testicle transversely, and found a number of vesicles filled with limpid liquor; and he remarked, that the Fallopian tube of this testicle was redder and somewhat longer than the other, as he had often observed in other animals when they were in season.

The left testicle was whiter, and its furface more smooth; for, though some vesicles were a little prominent, none of them were in the form of nipples; they were all similar to each other, and the corresponding Fallopian tube was nei|ther swelled nor red.

In the testicles of a girl, aged five years, he found the testicles with their vesicles, their blood-vessels, and their nerves.

In the testicles of a woman of sixty years, he discovered some vesicles, and the vestiges of a glandular substance, like large points of an ob|scure yellowish brown colour.

From all these observations, Valisnieri con|cludes, that the work of generation is carried on in the female testicles, which he continued to re|gard as ovaria, though he never could find any eggs in them, and though, on the contrary, he had discovered that the vesicles were not eggs. He says, likewise, that, for the impregnation of the egg, it is not necessary that the male semen should enter the uterus. He supposes, that the egg escapes through the nipple of the glandular body, after being impregnated in the ovarium; that it then falls into the Fallopian tube; that it gradually descends, and at last attaches itself to the uterus: He adds, that he is fully persuaded, that the egg is concealed in the cavity of the glandular body, though neither he nor any other anatomist was ever able to discover it.

In his estimation, the spirit of the male seed ascends into the ovarium, penetrates the egg, and gives motion to the foetus which previously existed in it. In the ovarium of the original mother of mankind, he observes, were eggs, which contained not only all the children she produced, but of the whole human race. If

this chain of infinite individuals contained in one, be incomprehensible to us, it is entirely owing to the imbecillity of our minds, of which we have daily proofs. But it is not, therefore, less consonant to truth, that all the animals which have existed, or can exist, were created at once, and were all included in their first mothers. The resemblance of children to their parents is owing, he continues, to the imagination, which acts so forcibly on the foetus as to produce stains, mon|strosities, disorder of parts, and extraordinary concretions, as well as perfect similarities.

This system of eggs, though it explains no|thing, and has no foundation in Nature, would have obtained the universal suffrages of physi|cians, if, nearly about the same time, another opinion had not sprung up, founded upon the discovery of spermatic animals.

This discovery, which we owe to Leeuwen|hoek and Hartsoeker, was confirmed by Andri, Valisnieri, Bourguet, and many other observers. I shall relate what has been advanced concern|ing those spermatic animals which are found in the semen of all males. Their number is so great, that the semen seems to be entirely com|posed of them; and Leeuwenhoek pretends to have seen many millions of them in a drop less than the smallest grain of sand. Though none of them appear in females, they are found in the emitted semen of all males, in the testicles, and in the vesiculae seminales. When the semen of

a man is exposed to a moderate heat, it thickens, and the motion of all the animalcules is sud|denly stopped. But, when allowed to cool, it dilutes, and the animals continue in motion till the liquor again thickens by evaporating. The more this fluid is diluted, the number of animalcules are augmented; and, when greatly diluted by the addition of water to it, the whole substance of the fluid seems to be composed of animals When the motion of the animalcules is about to cease, either on account of heat or of drying, they appear to approach nearer each other, to have a common circular motion in the centre of the small drop under observation, and to perish, all of them, at the same instant. But, when the quantity of liquor is greater, it is easy to distinguish them dying in succession.

These animalcules are said to be of different figures in different animals; but they are all long, thin, without any members, and move with rapidity in every direction. The fluid in which they are contained, as formerly remark|ed, is much heavier than blood. The semen of a bull, when chemically analyzed by Verrheyen, yielded first phlegm, then a considerable quan|tity of foetid oil, a very small proportion of vo|latile salt, and more earth than he expected* 1.26. This author was surprised that he could draw no spirit from the distillation of this liquor; and, as he imagined it contained a great quantity of

spirits, he attributed the evaporation of them to their subtility. But may we not suppose, with more probability, that it contains little or no spirits? Neither the consistence, nor the odor of this fluid, indicate the presence of ardent spirits, which never abound but in fermented liquors; and, with regard to volatile spirits, the horns, bones, and solid parts of animals, afford more of them than the fluids. What has received the appellation of seminal spirits, aura seminalis, a|mong anatomists, has, perhaps, no existence; and it is certain, that the moving bodies appa|rent in the seminal fluid, are not agitated by these spirits. But, that we may be enabled to pro|nounce more clearly concerning the nature of the semen, and of its animalcules, we shall pre|sent the reader with the principal observations which have been made on the subject.

Leeuwenhoek, having examined the semen of a cock, perceived a number of animals similar to river eels; but they were so minute, that 50,000 of them were not equal in bulk to a grain of sand. Of those in the semen of a rat, it re|quired, he says, many millions to make the thickness of a hair, &c. This excellent obser|ver was persuaded, that the whole substance of the semen was only a mass of animalcules. He saw these animalcules in the semen of men, of quadrupeds, of birds, of fishes, and of insects. In the semen of a grass-hopper, the animalcules were long, and extremely thin. They appeared,

he says, to be attached by their superior end; and the other end, which he calls their tail, had a brisk motion, like that of the tail of a serpent when its head is fixed. In the semen of young animals, when examined before they have any sexual appetite, he alledges that he saw the same minute animals, and that they had no motion: But, when the season of love arrived, the ani|malcules moved with great vivacity.

In the semen of a male frog, he saw animal|cules; but, at first, they were imperfect, and had no motion: Some time after, he found them alive. They were so minute, he observes, that ten thousand of them were only equal in bulk to a single egg of the female.

In the semen of a man and that of a dog, he pretended to see two species of animalcules, re|sembling males and females. Having shut up the semen of the dog in a small vial, he says, that a great number of animalcules died the first day; that, on the second and third day, still more of them died; and that few of them were alive on the fourth day. But, having repeated this experiment on the semen of the same dog, he found, at the end of seven days, the animal|cules as brisk and lively as if they had been newly extracted from the animal: And, having opened a bitch that, some time before the expe|riment, had been three times covered by the same dog he could not perceive, with his naked eye, any male semen in the uterus or its appendages;

but, by the assistance of the microscope, he found the spermatic animals of the dog in both horns of the uterus: In that part of the uterus which is nearest the vagina, he discovered great num|bers, which evidently proves, says he, that the male semen enters the uterus, or, at least, that the spermatic animals of the dog had arrived their by their own motion, which enables them to pass over 4 or 5 inches in half an hour. In the uterus of a female rabbit, which had just re|ceived the male, he observed an infinite number of spermatic animals. He remarks, that the bo|dies of these animals are round; that they have long tails; and that they often change their fi|gure, especially when the fluid in which they swim begins to dry up.

These experiments of Leeuwenhoek were re|peated by several people, who found them ex|actly consonant to truth. But Dalenpatius, and some others, who were inclined to exceed Leeu|wenhoek in acuteness of vision, alledged that, in the semen of a man, they not only found a|nimals resembling tadpoles, whose bodies ap|peared to be as large as a grain of corn, with tails about four times as long as their trunks, and who moved with great agility; but, what is still more amazing, Dalenpatius saw one of these animals break through its coat or covering: It was then no more an animalcule, but a real human body, in which he easily distinguished

the two arms and legs, the breast and the head* 1.27. But it is apparent, from the very figures, given by this author, of the embryo which he pretend|ed to have seen escape from its covering, that the fact is absolutely false. He believed that he saw what he describes; but he was deceived; for this embryo, according to his description, was more completely formed, at the time of its trans|migration from the condition of a spermatic worm, than it is in the uterus of the mother at the end of the fourth or fifth week. Hence this observation of Dalenpatius, instead of being confirmed by future experiments, has been re|jected by all naturalists, the most acute of whom have only been able to discover in the seminal fluid of man, round or oblong bodies, which ap|pear to have long tails, but no members of any kind.

One would be tempted to think that Plato had been acquainted with those spermatic animals which are transformed into men; for, at the end of his Timacus* 1.28, he says, 'Vulva quoque matrixque in foeminis eadem ratione animal avidum generandi, quando procul a foetu per aetatis fiorem, aut ultra diutius detinetur, aegre fert moram ac plurimum indignatur, passimque per corpus oberrans, meatus spiritus intercludit, respirare non sinit, extremis vexat angustiis, morbis denique omnibus premit, quousque u|trorumque

cupido amorque quasi ex arboribus foetum fructumve producunt, ipsum deinde de|cerpunt, et in matricem velut agrum inspar|gunt: Hinc animalia primum talia, ut nec prop|ter parvitatem videantur, necdum appareant formata, concipiunt; mox quae conflaverant, explicant, ingentia intus enutriunt, demum e|ducunt in lucem, animaliumque generationem perficiunt.' Hippocrates, in his treatise De Diaeta, seems likewise to insinuate that the se|men of animals is full of animalcules. Demo|critus talks of certain worms which assume the human figure; and Aristotle tells us, that the first men issued from the earth in the form of worms. But neither the authority of Plato, of Aristotle, of Hippocrates, of Democritus, nor of Dalenpatius, will ever be able to bestow credi|bility on a notion which is repugnant to the re|peated experience and observation of all those who have hitherto made inquiries into this sub|ject.

Valisnieri and Bourguet perceived small worms in the semen of a rabbit: One of their extremities was longer than the other; they were very active in their motions, and beat the fluid with their tails: Sometimes they raised them|selves to the top of the liquor, and sometimes sunk to the bottom; at other times they turned round, and twisted like serpents: In fine, says Valisnieri, I clearly perceived them to be real animals: 'E gli riconobbi, e gli giudicai senza

dubitamento alcuno per veri, verissimi, arcive|rissimi vermi* 1.29.' This author, though preju|diced in favour of the ovular system, admitted the actual existence of spermatic animals.

M. Andry pretends, that he could find no a|nimals in human semen previous to the age of puberty; that they exist not in the semen of very old men; that there are few of them in those who are affected with the venerial disease, and that these few are in a languishing state; that none of them appear alive in impotent per|sons; and that the animalcules in the semen of men have a larger head than those of other a|nimals, which corresponds, he observes, with the figure of the foetus and infant; and he adds, that those who use women too frequently have generally few or no animalcules in their semen.

Leeuwenhoek, Andry, and others, exerted e|very effort against the egg-system: They disco|vered in the semen of all males living animal|cules; they proved that these animalcules could not be regarded simply as inhabitants of this fluid, since the quantity of them was larger than that of the fluid itself; and since nothing simi|lar to them existed either in the blood, or in any other of the animal fluids: They maintained, that, as females furnished no animalcules, their fecundity was solely derived from the males; that the existence of living animals in the se|men throw more light upon the nature of gene|ration

than all the former discoveries on this subject; because the greatest difficulty in genera|tion is to conceive how life is first produced, the future expansion and growth of the parts being only accessory operations; and, consequently, that not a doubt remained of these animalcules being destined to become men, or perfect ani|mals, according to their species. When the im|probability was objected to them, that millions of animalcules, all equally capable of becoming men, should be employed for this purpose, while only one of them was to enjoy the singular ad|vantage of being admitted into the condition of humanity; when it was demanded of them, why this useless profusion of human germs? they replied, That it corresponded with the u|sual magnificence of Nature; that, in plants and trees, millions of seeds were produced, while only a few of them succeeded; and that, therefore, we ought not to be surprised at the prodigious number of spermatic animals. When the ex|treme minuteness of a spermatic worm, com|pared with the body of a man, was mentioned to them as a difficulty, they answered, that the seeds of trees, of the elm, for example, were e|qually minute, when compared with the perfect individuals; and they added, with equal pro|priety, metaphysical arguments, by which they proved, that largeness and minuteness were only relations, and that the transition from small to great, or from great to small, was performed by

Nature with greater facility than we could pos|sibly imagine.

Besides, they asked, are there not fre|quent examples of the transformation of in|sects? Do we not daily see small aquatic worms, by simply throwing off their skin or covering, from which they received their external figure, transformed into winged animals? May not spermatic animalcules, by a similar transforma|tion, become perfect animals? Every thing, therefore, they conclude, concurs in establishing this system of generation, and in overturning that which is founded on the notion of eggs; and, though eggs really existed in viviparous animals, as well as in the oviparous, these eggs would only be the matter necessary for the growth and expansion of the spermatic worm, which enters by the pedicle that attaches the egg to the ovarium, where it finds abundance of nourishment prepared for it. All the worms which are so unfortunate as to miss this passage through the pedicle into the egg, perish, and that one alone which finds the proper road, is trans|formed into a perfect animal. The difficulty of finding this passage is sufficient to account for the great number and apparent profusion of the spermatic animals. It is a million to one against any individual worm's finding this passage; but, to compensate this difficulty, there are more than a million of worms. When a worm has once got possession of an egg, no other can enter into

it; because, say they, the first worm shuts up the passage; or rather, there is a valve at the entry to the pedicle, which plays while the egg is not perfectly full; but, when the worm has filled the egg, this valve will not open, though push|ed by a second worm. Besides, this valve is exceedingly well contrived; for, if the worm should chance to descend through the passage by which it entered, the valve prevents its escape, and obliges it to remain till it be transformed. The spermatic worm then becomes a real foetus; and it is nourished by the substance of the egg, and the membranes serve it for a covering; and, when the nourishment contained in the egg be|gins to fail, the foetus attaches itself to the in|ternal surface of the uterus, and, by this means, extracts nourishment from the blood of the mo|ther, till, by its weight, and the increase of its strength, it at last breaks off all connection with the uterus, and issues into the world.

According to this system, it was not the first woman, but the first man, who contained all mankind in his own body. The pre-existent germs are no longer inanimate embryos locked up in eggs, and included, in infinitum, within each other. They are, on the contrary, small ani|mals, or organized living homunculi, included in each other in endless succession, and which, to render them men, or perfect animals, require nothing but expansion, and a transformation si|milar to that of winged insects.

As physicians are at present divided between the system of spermatic worms, and that of eggs, and, as every new writer upon generation has adopted either the one or the other of these hy|pothesis, it is necessary to examine them with care, and to show not only their insufficiency to ex|plain the phaenomena of generation, but that they rest upon suppositions which are entirely destitute of probability.

Both systems suppose an infinite progression, which, as formerly remarked, is a mere illusion of the brain. A spermatic worm is more than a thousand million of times smaller than a man. If, then, the body of a man be taken as an unit, the body of a spermatic worm will be expressed by the fraction 1/1000000000, i. e. by a number consisting of ten cyphers; and, as man is to a spermatic worm of the first generation in the same proportion as this worm is to a worm of the second generation, the size of this last sper|matic worm will be expressed by a number con|sisting of 19 cyphers; for the same reason, the size of a spermatic worm of the third generation must be expressed by a number consisting of 28 cyphers, that of the fourth generation by 37 cyphers, that of the fifth generation by 46 cy|phers, and that of the sixth generation by 55 cyphers. To form an idea of the minuteness represented by this fraction, let us take the di|mensions of the sphere of the universe from the Sun to Saturn; and, supposing the Sun to be a

million of times larger than the Earth, and di|stant from Saturn a thousand solar diameters, we shall find that 45 cyphers are sufficient to express the number of cubic lines contained in this sphere; and, if we reduce each cubic line into a thousand million of atoms, no more than 54 cyphers will be necessary to express their number: Of course, a man will be proportional|ly greater, when compared with a spermatic worm of the sixth generation, than the sphere of the universe when compared to the smallest atom that can be seen with the assistance of a microscope. But, if this calculation were carried on to the 16th generation, the minuteness would exceed all powers of expression. It is apparent, therefore, that the probability of this hypothesis vanishes in proportion as the object dininishes. This calculation applies equally to eggs as to spermatic worms; and the want of probability is common to both. It will, no doubt, be ob|jected, that, as matter is infinitely divisible, this gradual diminution of size is not impossible. To this I reply, that all infinities, whether in geometry or in arithmetic, are only mental ab|stractions, and have no actual existence in Na|ture. If the infinite divisibility of matter is to be regarded as an absolute infinite, it is easy to demonstrate, that, in this sense, it has no ex|istence; for, if we once suppose the smallest pos|sible atom, by the very supposition, this atom must be indivisible; because, if it were divisible,

it would not be the smallest possible atom, which is contrary to the supposition. It is, therefore, apparent, that every hypothesis which admits an infinite progression ought to be rejected not only as false, but as destitute of every vestige of probability; and, as both the vermicular and ovular systems suppose such a progression, they should be excluded for ever from philosophy.

These systems are liable to another objection: In the ovular system, the first woman contain|ed both male and female eggs; the male eggs could only give origin to males; but the female eggs behoved to contain millions of generations of both males and females: Hence every wo|man must have always contained a certain num|ber of eggs capable of being unfolded in infini|tum, and another number, which could only be unfolded once, and could have no farther ope|ration in the series of existence. The same thing must take place in the vermicular system. Hence we may conclude, that there is not the smallest degree of probability in hypotheses of this nature.

A third difficulty still remains, arising from the resemblance of children sometimes to the father, sometimes to the mother, and sometimes to both, and from the evident characters of spe|cific differences in mules and other monstrous productions. If the foetus proceeds from the spermatic worm of the father, how comes the child to resemble its mother? If the foetus pre|exists

in the egg of the mother, how should the child resemble its father? And, if the spermatic worm of a horse, or the egg of a she-ass, be the origin of the foetus, how should the mule par|take of the nature and figure both of the horse and ass?

These general objections, though perfectly invincible, are not the only difficulties with which these systems are embarrassed. May it not be demanded of those who embrace the ver|micular system, how these worms are trans|formed, and wherein consists the analogy be|tween this transformation and that which insects undergo? The caterpillar which is to become a butterfly, passes through a middle state, and, after it ceases to be a chrysalis, is completely formed, has acquired its full growth, and is instantly capable of generating: But, in the pretended transformation of the spermatic worm of a man, there is no middle or chrysalis state; and, sup|posing this to happen during the first days of conception, why is not the production of this chrysalis, in place of an unformed embryo, a perfect adult? Here all analogy ceases; and, of course, the notion of the transformation of the spermatic worm can receive no support from this quarter.

Besides, the worm which is to be transformed into a flie proceeds from an egg; this egg is produced by the copulation of the male and fe|male, and it includes the foetus which is to pass

into a chrysalis, before it arrives at the perfect state of a flie, and before it acquires the power of generating. But the spermatic worm has no generative faculty; neither does it proceed from an egg: And, though it should be supposed that the semen contains eggs which produce the sper|matic animals, the same difficulty still remains; for these supposed eggs are not a result of the copulation of two sexes, like those of insects. Con|sequently, the analogy fails here likewise; and the transformation of insects, in place of strength|ening this hypothesis, seems entirely to destroy it.

The seeds of vegetables are resorted to, in or|der to account for the infinite number of sper|matic animals: But this analogy does not ap|ply; for, all the spermatic animals, one only ex|cepted, must absolutely perish. The seeds of vegetables, however, are not subject to the same necessity. When they become not vegetables themselves, they nourish other organized bodies, and serve the purposes of growth and of repro|duction to animals. But the prodigious super|fluity of spermatic animals can answer no end whatever. I make this remark, purely because I wish to omit nothing that has been advanced on the subject; for I acknowledge, that no ar|gument drawn from final causes can either establish or destroy a physical theory.

The apparent equality in the number of sper|matic animalcules in all animals, has also been

objected to by the supporters of this doctrine. If these animalcules are the immediate cause of generation, why is there no proportion between their numbers and those of the young, which are various in men, quadrupeds, birds, fishes, and insects? Besides, there is no proportional difference in most species of spermatic animals, those of a rat being nearly equal in size to those of a man. Even when a difference in size takes place, it has no proportion to the bulks of the animals. The spermatic animals of the calmar, which is a small fish, are a hundred thousand times larger than those of a man or of a dog. This is an additional proof that these worms are not the sole and immediate cause of genera|tion.

The particular objections to the ovular system are not less weighty. If the foetus existed in the egg before the junction of the male and female, why do we not see the foetus in the egg before impregnation, as clearly as after it? We formerly mentioned, that Malpighius always found the foetus in eggs which had received the impregnation of the male, and could discover nothing but an unformed mole or mass in the cicatrice of unimpregnated eggs. It is, there|fore, evident, that the foetus is never formed till the egg has been impregnated.

Farther, we not only cannot discover the foe|tus in eggs before the intercourse of the sexes, but we have not been able to demonstrate the

existence of eggs in viviparous animals. Those physicians who pretend that the spermatic worm is the foetus inclosed in a coat or covering, are at least ascertained of the existence of spermatic worms; but those who maintain that the foetus pre-exists in the egg, have no evidence of the existence of the egg itself; for the probability of their non-existence in viviparous animals a|mounts almost to a certainty.

Though the partizans of the ovular system agree nto as to what ought to be regarded as the real egg in the testicles of females, they all allow, however, that impregnation is accomplished in the testicles or ovarium. But they never con|sider, that, if this were the case, most foetuses would be found in the abdomen in place of the uterus; for, as the superior extremity of the Fallopian tube is unconnected with the ovarium, the pretended eggs would often fall into the ab|domen. Now, we know this to be at least a very rare phaenomenon; and it is probable that it never happens but by means of some violent accident.

These objections and difficulties have not e|scaped the ingenious author of Venus Physique. But, as his work is in the hands of the public, and as it admits not of abridgement, we shall refer the reader to the book itself; and shall conclude with an account of a few particular experiments, some of which appeared to favour and others to contradict the above systems.

In the history of the Academy of sciences, ann. 1701, some objections are proposed by M. Mery against the egg-system. This able anato|mist maintained, with propriety, that the vesicles found in the testicles of females are not eggs; that they adhere so firmly to the internal surface of the testicle, as not to admit of a natural sepa|ration; and that, though they could separate from the substance of the testicle, it was impos|sible for them to get out of it, because the tex|ture of the common membrane inclosing the whole testicle is so firm and strong, that it is im|practicable to conceive the possibility of its being pierced by a vesicle or round soft egg. And, as most anatomists and physicians were prepos|sessed in favour of the egg-system, and imagined that the number of cicatrices in the testicles cor|responded with the number of foetuses, M. Mery showed such a quantity of these cicatrices in the testicles of a woman, as, upon the supposition of the truth of this system, would have argued a fecundity beyond the power of credibility. These difficulties stimulated other anatomists of the academy, who were partizans of the eggs, to make new researches. M. Duverney ex|amined the testicles of cows and sheep, and maintained, that the vesicles were eggs, because some of them adhered less firmly to the testicles than others; and that it was natural to suppose that they separated altogether when they arrived at full maturity; especially as by blowing into

the cavity of the testicle, the air passed between the vesicles and the adjacent parts. M. Mery simply replied, that this proof was insufficient, as these vesicles were never seen separate from the testicles. M. Duverney farther remarked the glandular bodies upon the testicles; but he never considered them as parts essential to ge|neration, but as accidental excrescences, like gall-nuts on the oak. M. Littre, whose preju|dices in favour of eggs were still stronger, maintained, not only that the vesicles were eggs, but even assured us, that he discovered in one of them a well formed foetus, of which he could distinguish both the head and trunk; and he has even given their dimensions. But, admitting this wonder, which never appeared to any eyes excepting his own, to be convinced of the doubt|fulness of the fact, we have only to peruse his memoir* 1.30. From his own description it appears, that the uterus was schirrous, and the testicle very much corrupted; that the vesicle or egg, which contained the pretended foetus, was much less than ••••mmon, &c.

Nuck furnishes us with a celebrated experi|ment in favour of eggs. He opened a bitch three days after copulation; he drew out one of the horns of the uterus, and tied it in the middle so as to prevent the superior part of the Fallopian tube from having any communication with the inferior part. After this he replaced the horn of

the uterus, and closed the wound. Twenty-four days afterwards, he again opened the wound, and found two foetuses in the superior part of the tube, that is, between the testicles and the ligature; and there was no foetus in the un|der part. In the other horn of the uterus, that was not tied, he found three foetuses regularly disposed; which proves, says he, that the foetus proceeds not from the male-semen, but that it exists in the egg of the female. Supposing this experiment, which is single, had been often re|peated with the same success, the conclusion the author draws from it is not legitimate: It proves no more than that the foetus may be formed in the superior part of the horn of the uterus, as well as in the inferior; and it is natural to think that, by the pressure of the ligature, the seminal liquor in the inferior part was forced out, and, of course, frustrated the work of generation in that region of the uterus.

This is all the length that anatomists and phy|sicians have proceeded in the subject of genera|tion. It only remains that I deliver the results of my own experiments and inquiries; and I shall leave the reader to judge whether my sy|stem be not infinitely more consonant to nature than any of those of which I have given an ac|count.

CHAP. VI.

Experiments on Generation.

I Often reflected on the above two systems of generation, and was daily more and more convinced that my theory was infinitely more probable. At length I began to suspect that these living organic particles, from which I thought all animals and vegetables derived their origin, might be recognized, by the assistance of good glasses. My first notion was, that the spermatic animalcules found in the seminal fluid of all males, might probably be these very organic particles; and I reasoned in this manner. If all animals and vegetables contain an infinite num|ber of organic particles, these particles should be most abundant in their seeds, because the seed is an extract from all the organic parts, and espe|cially from those which are most analogous to the individual: Perhaps the spermatic animals found in the semen of males may actually be those very organic particles, or at least, the first union or assemblages of them. But, if this be the case, then the semen of females ought to contain or|ganic living particles, or animalcules, similar to

those of the male. They ought, for the same reason, to be found in the seeds of plants, in the nectarium, and in the stamina, which are the most essential parts of vegetables, and contain the or|ganic particles necessary for their reproduction. I therefore determined to examine with the microscope the seminal liquors of males and fe|males, and the germs of plants; and, at the same time, I imagined that the cavities of the glandu|lar bodies of the uterus might be the reservoirs of the female semen. Having communicated my ideas of this subject to my ingenious friends Mr Needham, M. Daubenton, M. Gueneau, and M. Dalibard, they encouraged me to commence a set of experiments in order to throw light up|on this mysterious operation of nature. All of these gentlemen occasionally attended and assisted me; but particularly M. Daubenton, who was never absent, and who was witness to every ex|periment I made.

I employed a double microscope, which I had from Mr Needham, being the same with which he made his numerous and ingenious observa|tions * 1.31. This instrument is infinitely preferable to those employed by Leeuwenhoek* 1.32.

EXPERIMENT I.

Having procured the seminal vessels of a man who died a violent death, and whose body was still warm, I extracted all the liquor from them, and put it in a vial. I examined, by the micro|scope, a drop of this liquor, without any dilution. As soon as the vapours, which arose from the liquor, and obscured the glass, were dissipated, I observed pretty large filaments [plate I. fig. 1.], which, in some places, spread out into branches, and, in others, intermingled with each other. These filaments clearly appeared to be agitated with an internal undulatory motion, like hollow tubes, which contained some moving substance. I saw distinctly [pl. I. fig. 2.] two of these fi|laments, which were joined longitudinally, se|parate from each other in the middle, and alter|nately approach and recede, like two stretched cords, fixed by the ends, and drawn asunder at the middle. These filaments were composed of globules which touched one another, and resem|bled a chaplet of beads. I then observed fila|ments [pl. I. fig. 3.] which were blown up, and swelled in certain places, and perceived small oval globules issue from these swelled parts, which had a vibratory motion, like that of a pendulum [pl. I. fig. 4.] These small bodies were attached to the filament by little threads,

which gradually lengthened as the bodies mo|ved: And, lastly, I observed these small bo|dies detach themselves entirely from the large filament, and draw after them the little thread, which resembled a tail. As the liquor was too thick, and the filaments too near each other, I diluted another drop with pure rain water, after satisfying myself that it contained no animal|cules. I then perceived that the filaments were more distant from each other, and saw distinctly the motion of the small bodies above taken no|tice of, [pl. I. fig. 5.] which was more free, and they appeared to swim with greater agility, and trailed their threads after them with greater ease; and, if I had not seen them separate from the filaments, and draw the threads out of them, I should have believed, from this second obser|vation, the moving bodies to be real animals, and their threads to be tails. After examining with great attention one of the filaments, which was three times thicker than the small bodies, I per|ceived two of those bodies detach themselves with much difficulty, and drag after them long slender threads, which impeded their motion.

This seminal liquor was at first too thick. But it gradually became more fluid, and, in less than an hour, it was almost transparent; and, in proportion as its fluidity augmented, the phae|nomena changed, in the manner to be just men|tioned.

EXPER. II.

When the seminal liquor became more fluid, the filaments disappeared; but the small bodies were exceedingly numerous [pl. I. fig. 6.]. Their motion, for the most part, resembled that of a pendulum; each of them had a long thread, from which they evidently endeavoured to disengage themselves; their progressive mo|tion was extremely slow, during which they vibrated to the right and left. At each vibration, they had a rolling unsteady motion; so that, besides their horizontal vibrations, they roll or vibrate in a vertical direction; which proves these bodies to be of a globular figure, or at least that their inferior part is not a flat base sufficiently extensive to keep them in one position.

EXPER. III.

At the end of two or three hours, when the liquor was more fluid, a still greater number of these moving bodies appeared [pl. I. fig. 7.]. They were more free of incumbrances; their threads were shorter; their progressive motion was more direct; and their horizontal vibration was greatly diminished; for the longer the threads are, their vibratory motion was increased,

and their progress forward was diminished. The vertical vibration was still apparent.

EXPER. IV.

In five or six hours, the liquor had almost all the fluidity it could acquire, without being de|composed. We then discovered [pl. II. fig. 8.] that most of these small moving bodies were en|tirely disengaged from their threads. Their fi|gure was oval: They moved forward with con|siderable quickness; and, by their motion back|ward and forward, and to every side, they had now more than ever the appearance of real ani|mals. Those which had tails or threads sticking to them, seemed to have less vivacity than the others. Of those which had no threads, some ap|peared to change both their figure and their size. Some of them were round; but the greatest part of them were oval, and a few of them were thicker at the extremities than in the middle. The rolling and vibratory motions were still per|ceptible.

EXPER. V.

In 12 hours, the liquor had deposited, at the bottom of the vial, a kind of gelatinous, bluish, or rather ash-coloured substance; and the fluid

that swimmed on the top was nearly as clear as water, only it had a tincture of blue, like water in which a small quantity of soap has been dis|solved. It still, however, retained its viscosity. The little bodies, which were now entirely freed from their threads, moved with great activity on all sides, and some of them turned round their centres. Most of them were oval, though some of them were round. I have seen them change figures, and from oval become round: I have seen them divide, and, from a single oval or globule, separate into two. Their activity always in|creased as their size diminished.

EXPER. VI.

At the end of 24 hours, the liquor had depo|sited a greater quantity of gelatinous matter, which I diluted, with some difficulty, in water. It appeared to consist of a multitude of opaque tubes, resembling lace, but without any regula|rity or the smallest motion. In the clear semen itself, there were a few small bodies still moving; next day their number was still farther dimi|nished. After this, nothing was to be seen but globules without the least appearance of motion.

These experiments were often repeated with great exactness; and they convinced me that the threads which adhere to the moving bodies are not tails, nor any part proper to these bodies;

[figure]

Plate 3.

for the tails or threads have no proportion to the rest of the body; they are of different di|mensions, though the bodies are always nearly of the same size at the same time. The motion of the globule is embarrassed in proportion to the length of the tail. When the tail is too long, it sometimes prevents the progressive motion al|together, leaving nothing but the vibrations from right to left; and the globules make evident essorts to disentangle themselves from this in|cumbrance.

EXPER. VII.

Having procured the seminal fluid of another man recently dead, I put a pretty large drop of it on the glass, which soon liquified without any mixture. It had the appearance of a close net|work, the filaments of which were of a conside|rable length and thickness, and they seemed to proceed from the thickest part of the liquor, [pl. II. fig. 9.]. These filaments separated in proportion as the liquor became more fluid; and at last they divided into globules, which seemed at first to have too little force to put them in motion: But their power of moving increased as they receded from the filaments, and they ap|peared to make considerable efforts to disengage themselves. In this manner each of them gra|dually drew tails of different lengths out of the

filaments. Some of these tails were so long and so thin, that they had no proportion to the bo|dies, which were always more or less embarras|sed, according to the length of the threads or tails. When the tail was long, the angle of the vibratory motion was increased; and, when the tail was short, the progressive motion was more conspicuous.

EXPER. VIII.

I continued my observations, almost without interruption, for 14 hours, and I discovered, that the length of the tails or threads gradually dimi|nished, and became so thin and delicate, that their extremities successively ceased to be visible; and at last the whole disappeared. The horizontal vibrations of the globules then ceased, and their progressive motion was direct, though they still had vertical oscillations, or rather, they rolled like a vessel at sea. The small bodies, when de|prived of their tails, were oval and transparent, and resembled those pretended animals which are seen in oyster-water on the 6th or 7th day, or those found in the jelly of roasted veal at the end of the 4th day.

EXPER. IX.

Between the 10th and 12th hour, the liquor was become very fluid, and all the globules ap|peared

to proceed in troops from one side of the drop [pl. II. fig. 10.]. They passed over the field of the microscope in less than four seconds; they marched in lines of seven or eight in front; and succeeded each other without interruption, like the defiling of soldiers. I observed this sin|gular phaenomenon for more than five minutes; and, as the current of animals did not then cease, I was desirous of discovering the cause. I there|fore gently shifted the glass, and perceived that all these moving globules proceeded from a kind of mucilage, [pl. II. fig. 11.] or net-work of fi|laments, which continually produced them, and with more rapidity and copiousness than the fila|ments had done ten hours before. There was still a difference more remarkable between the globules produced by the liquor when thick, and those produced when it was more fluid; for, in the latter case, they drew no threads or tails af|ter them, their motion was quicker, and they went in flocks like sheep. I examined the mu|cilage from which they proceeded for a long time, and perceived that it gradually diminished and was converted into moving globules, till more than one half of it was destroyed. After which, the liquor being too dry, this mucilage became obscure in the middle, and it was sur|rounded with small threads, forming square inter|vals, [pl. II. fig. 12.]. These small threads seem|ed to be composed of the bodies of the moving globules which had been killed by the drying of

the liquor, and the whole resembled the web of a spider besprinkled with drops of dew.

EXPER. X.

By the first experiments, I perceived that these small moving bodies changed their figures; and I imagined, that, in general, they diminished in bulk, though I was not then altogether certain of the fact. But my subsequent observations removed every doubt. At the 12th and 13th hour, the bodies were visibly smaller; but, as they diminished in bulk, their specific gravity in|creased, especially when they ceased to move, which they generally did all at once, and fell down to the bottom in the form of an ash-co|loured sediment, which was perceptible by the naked eye; and, by the assistance of the micro|scope, it appeared to be composed of globules attached to one another, sometimes by threads, and at other times in groups, but always in a re|gular manner.

EXPER. XI.

Having procured the fresh semen of a dog, I observed that this liquor was clear, and had very little tenacity. I examined it without the addition of water, and I perceived moving bodies

[figure]

Plate 4.

almost entirely similar to those in the human semen, [Pl. III. fig. 13.]. Their tails and their form were almost precisely the same with those represented in Pl. II. fig. 7. where the liquor had been liquified for two or three hours. I in vain searched this liquor for the silaments which appear|ed in that of men. I only remarked some long and very delicate threads, exactly similar to those which served for tails to the globules. These threads contained no globules; neither had they any motion. The globules with tails seemed to move with more vivacity than those in the hu|man semen. They had hardly any horizontal vibrations; but they always rolled vertically. Their number was not great; and, though their progressive motion was quicker, they took up some time in passing over the field of the micro|scope. I examined this liquor during three hours, and could observe no change. I conti|nued my examination, from time to time, for several days, and remarked, that the number of moving bodies gradually diminished. On the second day, the greatest part of them had lost their tails: On the third, very few of them re|tained their tails; on the fourth, however, some tails still adhered. The liquor had now de|posited a whitish sediment, which appeared to be composed of globules without motion, and some small threads that seemed to be the tails which had separated from the globules. Some globules appeared to have dead ones attached to

them; for their figure differed from that of those in motion, [Pl. III. fig. 14.]: They were larger than the moving globules, or the dead ones at the bottom of the liquor, and seemed to have a kind of fissure or opening.

EXPER. XII.

At another time I examined the seminal fluid of the same dog, and perceived the same phae|nomena which have been described. I farther observed, in a drop of this liquor, a mucilaginous part, [Pl. III. fig. 15.] from which globules is|sued as in Exper. IX. and these globules formed a current, and moved in regular troops. This mucilage appeared to be agitated internally with a swelling or undulating motion, which produced small protuberances in different parts; and these protuberances issued suddenly in the form of globules, which moved briskly forward in the same direction. These globules differed not from the others, excepting that they issued from the mu|cilage without tails. Some of them, I remarked, changed their figure; they lengthened them|selves till they resembled small cylinders; after which the extremities of the cylinders swelled, and divided by the middle into two globules, and both of them moved on in the same direction with the rest.

EXPER. XIII.

The small glass which contained this liquor having been overturned by accident, I took, from the same dog, another quantity of semen. But, whether the animal had been fatigued by two frequent emissions, or from some other cause, this seminal liquor contained nothing: It was transparent and viscous, like the serum of blood; and, though I examined it, at different times, for 24 hours, I could perceive no moving bo|dies, no mucilage, nor, in a word, any thing si|milar to what I had formerly seen.

EXPER. XIV.

I then opened a dog, and took out the testicles, and the vessels adhering to them. But I remark|ed, that he had no seminal vessels: The seed of this animal probably passes directly from the testicles into the urethra. Though the dog was full grown and vigorous, I found very little se|men in the testicles. I examined with the mi|croscope the small quantity I could collect; but could perceive no moving bodies: I only saw a great number of very minute globules, the greatest part of which were motionless; and some of the smallest of them seemed to move towards each other. But of this I could not be

certain; because the small drops dried in a mi|nute or two after they were put upon the glass.

EXPER. XV.

I cut the testicles of this dog into two parts, put them into a glass-vessel, with as much wa|ter as was sufficient to cover them, and corked up the glass. Three days after, I examined this infusion with a view to discover if the flesh con|tained any moving bodies, and I perceived in the water of this infusion a great number of moving bodies, some of them of a globular, others of an oval figure, and entirely resembling those I had seen in the seminal fluid of the dog, excepting that they had no threads or tails: They moved in all directions with great viva|city. I observed, during a long time, these bo|dies, which appeared to be animated, and I per|ceived several of them change their figures be|fore my eyes. Some of them lengthened, o|thers contracted, and others swelled at the two extremities. The whole of them seemed to turn on their centres; some of them were larger, and others smaller; but the whole were in mo|tion, and resembled, both in size and figure, those which were described in Exper. IV.

EXPER. XVI.

Next day, the number of moving globules was still increased; but they were smaller; their motion more rapid and more irregular; and their form and manner of moving were dif|ferent, and appeared to be more confused: The day after, and the following days, till the 20th, moving bodies still appeared in this water. They daily diminished in size, and at last became so small that they could be hardly perceived; but the last of them I was able to distinguish on the 18th and 20th days, moved with the same ra|pidity as ever. On the top of the water there was a pellicle which appeared to be composed of the skins or coverings of the moving bodies, of small threads, &c. But no motion appeared in it. This pellicle and the moving bodies could not be introduced into the liquor by means of the external air; for the bottle was always closely corked.

EXPER. XVII.

I opened successively, on different days, ten rabbits, in order to examine their seminal fluid. In the first, second, and third, I found not a single drop, either in the testicles or seminal ves|sels, though I was certain that two of them were

fathers of a numerous progeny. I imagined that the presence of the female might be neces|sary for the secretion of the semen; I therefore put males and females by pairs into separate cages, so constructed that they could not possibly copulate. Neither did this scheme at first suc|ceed; for I opened two of them without finding any semen. In the sixth, however, which was a large white rabbit, full of vigour, I found as much liquor in the seminal vessels as would fill a small coffee-spoon. This matter resembled the jelly of meat, was of a citron colour, and almost transparent. Having examined it with the microscope, it gradually separated into fila|ments and large globules, several of which were attached to each other like a string of beads; but I could discover no distinct motion; only, as the matter dissolved, it formed a kind of current, by which the filaments and globules were carried down to one side of the glass. I waited till the matter should become more fluid; but I was dis|appointed; for, after liquifying a little, it dried up, and I could observe nothing farther than what I have already described. I then added water to it, but without success; for the water seemed not to penetrate or dilute the matter.

EXPER. XVIII.

I opened another rabbit, and found only a small quantity of seminal matter, which had hardly

any of the yellow colour, and was more fluid than the former. As the quantity was very small, I was apprehensive lest it should dry too suddenly; I therefore instantly mixed it with water, and could perceive in it neither the fila|ments nor the strings of beads that I had obser|ved in the other; but I discovered the large globules, and farther remarked, that they had a kind of trembling restless motion. They had also a progressive motion; but it was very slow: Some of them moved round others, and most of them appeared to turn round their centres. I could proceed no farther in my observations, because the liquor dried suddenly up.

EXPER. XIX.

Having dissected another rabbit, that had been placed in the same circumstances, I found no seminal liquor; but, in the seminal vessels of another, I found nearly as much congealed mat|ter as in Exper. XVII. I examined this matter without discovering any thing. I therefore took the whole, and, adding to it a double quantity of water, shook the mixture violently in a glass. I then left it to settle for ten minutes; after which I examined a drop taken from the surface, and perceived the large globules formerly men|tioned; but they were few in number, and per|fectly detached from one another. They moved

towards each other; but this motion was so slow, as to be hardly perceptible. Two or three hours after, the globules seemed to be diminished in size; their motion was more sensible; and they turned upon their centres. Though their trem|bling was more apparent than their progressive motion; yet they plainly changed places in an irregular manner, with respect to each other. In six or seven hours, the globules were become smaller, and their activity was greater. Their number appeared to be great, and all their mo|tions were sensible. Next day there was a pro|digious multitude of moving globules, and they were at least three times less than at first. I continued my observations for eight days, and I perceived that several of the globules joined; and, though all motion ceased after this union, it appeared only to be superficial and accidental. Some of them were larger, and others less; though most of them were spherical, some of them were oval, and others cylindrical. The largest were most transparent; and the smallest were almost black. This difference could pro|ceed from no accident in the light; for they were always of the same colour, whatever was their situation: The motion of the small globules was likewise more rapid. The whole gradually diminished in size, so that, on the eight day they were so small that it was with the utmost diffi|culty I could distinguish them, and at last they totally disappeared.

EXPER. XX.

In fine, having, with great difficulty, procured the seminal liquor of another rabbit, in the very state in which it is conveyed into the female, I remarked, that it was much more fluid than that which was extracted from the seminal vessels; and the phaenomena it presented were also very different: For, in this liquor there were moving globules, filaments without motion, and a kind of globules with tails or threads, similar to those in the seminal fluid of man and of the dog, only these last appeared to be less, and more active [Pl. III. fig. 17.]. They traversed, in an instant, the field of the microscope: Their tails seemed to be much shorter than those of other spermatic animals; and I acknowledge, that I was uncer|tain whether some of these tails were not decep|tions occasioned by the track of the globules in the liquor; for they moved with such rapidity, that I could hardly observe them; and besides, the liquor, though sufficiently fluid, dried very suddenly.

EXPER. XXI.

Having procured, at different times, the testi|cles and seminal vessels of 12 or 13 rams, re|cently after they were killed, I could not sind,

either in the epidydimis or seminal vessels, a quantity of semen sufficient for observation. In the small drops I could collect, I found nothing but globules without motion. As these experi|ments were made in March, I imagined that, by repeating them in October, which is the time of rutting, I might find more liquor in the vessels. I cut several testicles in two longitudinally, and having collected a small drop of liquor, I still could perceive nothing but motionless globules of different sizes.

EXPER. XXII.

I took three testicles of three different rams, cut them into four parts, and put each of them into a glass-vessel, with as much water as was sufficient to cover them, and then shut the vessels so close as to exclude the air. I allowed the testicles to infuse during four days; after which I examined the liquor in each glass with the mi|croscope, and found the whole full of moving bodies, most of which were oval, and some of them globular. They were equally large, and greatly resembled those described in Exper. VIII. Their motion was not rapid, but equal, uniform, and in all directions. In each liquor, the mo|ving bodies were nearly of the same size; but, in the one they were larger, in the other less, and, in the third, still more minute: They had no

tails; neither were there, in the liquor, any threads or filaments. They often changed their figures, and seemed successively to cast their skin or outer covering. They daily became smaller, and, on the 16th day, they were so small as scarcely to be visible.

EXPER. XXIII.

In the following October, I opened a ram, and found a great quantity of seminal liquor in the epidydimis. Having examined it with the microscope, I saw such an innumerable multi|tude of moving bodies, that the liquor seemed to be entirely composed of them. As the liquor was too thick, I diluted it with water; but I was astonished to find, that the water had stopped all motion in the bodies; though I saw them di|stinctly in the liquor, they were all at absolute rest. Having frequently repeated the same ex|periment, I discovered, that cold water, which diluted the seminal liquors of other animals, made that of the ram coagulate.

EXPER. XXIV.

I then opened another ram, and, to prevent the liquor from coagulating by cold, I left the parts of generation in the body of the animal,

which was covered with warm cloths. This pre|caution assorded me an opportunity of exami|ning with ease the seminal liquor of many rams in its fluid state. It was filled with an infinite number of oblong moving bodies, [pl. III. fig. 18.] which run about in every direction. But, when|ever the liquor cooled, all motion instantly ceased; so that I could never observe the same drop above a minute or two. When I diluted the liquor with warm water, the bodies conti|nued to move for three or four minutes. The moving bodies were so numerous, that, though the liquor was diluted, almost all of them touch|ed each other. They were all of the same size and figure. None of them had tails. Their motion was not rapid; and, when the liquor began to coagulate, they suffered no change in their form.

EXPER. XXV.

As I was persuaded, both by my theory, and the experiments made by others upon this sub|ject, that the female, as well as the male, posses|sed a prolific seminal fluid; and, as I had no doubt but that the glandular bodies of the testi|cles, where prejudiced anatomists had in vain searched for the egg, were the reservoirs of this fluid; I purchased several dogs and bitches, and male and female rabbits, which were kept sepa|rate

from each other: And, that I might have an object to compare with the female fluid, I a|gain examined the seminal liquor of a dog, which had been emitted in the natural manner. I found the moving bodies in the same state and attended with the same circumstances as former|ly [pl. IV. fig. 19.].

EXPER. XXVI.

A live bitch was next dissected, which had been four or five days in season, without having any communication with the male. The testicles were as large as silberds. On one of them I found a red prominent glandular body of the size of a pea, which had a perfect resemblance to a little nipple, with a visible fissure, that had two lips, one of which was more prominent than the o|ther. Having opened this fissure, a liquor di|stilled from it, which we collected for exa|mination. The testicles were then returned into the body of the animal, which was still alive, in order to preserve them from cold. I then examined this liquor with the microscope, and had the satisfaction of perceiving, at the first glance, moving bodies with tails, exactly similar to those which we had observed in the seminal fluid of the dog [pl. IV. fig. 20.]. Messrs Need|ham and Daubenton, who were present, were so struck with this resemblance, that they could not

be persuaded that the spermatic animals were not the very same; and they imagined that I had forgotten to change the object-glass, or rather, that the same pick-tooth with which the drops of the female fluid were collected, had also been employed in collecting those of the male. Mr Needham, therefore, changed both the object-glass and the pick-tooth, and took a fresh drop from the fissure of the glandular body, and exa|mined it first with his own eyes. He again saw the very same moving bodies, and was fully convinced, not only of the existence of sperma|tic animals in the seminal fluid of the female, but also of their resemblance to those in the se|men of the male. We repeated the experiment with fresh drops no less than ten times, in all of which the phaenomena were exactly the same.

EXPER. XXVII.

Having then examined the other testicle, I found an unripe glandular body, which was smaller, and less red than the former, and had no fissure; but, after opening it with a scalpel, I found no liquor. Upon the external surface of this testicle, there were some lymphatic vesi|cles. I pierced one of them with a lancet, and there issued a clear liquor, to which I imme|diately applied the microscope. But it con|tained nothing similar to what we discovered in

[figure]

Plate V.

that of the glandular body. It was a transparent liquor, composed of very small globules, with|out any motion. After repeating this experi|ment several times, I was convinced, that the li|quor in the vesicles is only a species of lymph, which contains nothing animated or similar to what we perceive in the female semen, which is secreted and matured in the glandular bodies.

EXPER. XXVIII.

Some time after, another bitch was opened, which had been seven or eight days in season, and had not received the male. I examined the testicles, and upon each I found a glandular bo|dy in full perfection. The first was half open, and had a canal which penetrated the testicle, and was full of seminal fluid; the second was larger and more prominent, and the fissure or canal that contained the fluid was below the nip|ple, which protruded outward. I took the li|quor out of both the glandular bodies, and, on comparison, found them entirely similar. This seminal liquor of the female is equally fluid with that of the male. After examining the liquors extracted from each testicle, I found in them the very same moving bodies [pl. IV. fig. 21.]. I perceived at leisure the same phaenomena that I had observed in the seminal liquor of the other bitch; I saw several globules which moved with

great rapidity, which endeavoured to disengage themselves from the mucilage that surrounded them, and which dragged tails or threads after them. Their number was equally great with that in the male semen.

EXPER. XXIX.

I squeezed the whole liquor out of these two glandular bodies, and put it into the glass of a watch. The quantity was sufficient to serve for four or five hours observation. I remarked that it deposited a kind of sediment, or at least began to thicken. I took a drop of the thickest part of the liquor, and having examined it, I disco|vered that the mucilaginous part of the semen was condensed, and formed a kind of net-work. From the anterior edge of this net-work, there issued a current of globules which moved with great rapidity [Pl. IV. fig. 22.]. These globules were extremely active and lively, and they ap|peared to be divested of their mucilaginous co|verings, and of their tails. This stream of glo|bules resembled the motion of the blood in the veins; for they seemed not only to be animated, but to be pushed on by some common force, which obliged them to follow each other in troops or rows. From this experiment, and from the 11th and 12th, I concluded, that, when the fluid begins to coagulate or grow thick, the ac|tive

globules break their mucilaginous covering, and escape at that side where the liquor is most fluid. They had no threads or tails, and most of them were oval, and seemed to be flat below; for they had no rolling motion.

EXPER. XXX.

I opened the horns of the uterus longitudinal|ly, and having squeezed a little liquor out of them, I found it exhibited precisely the same phaenomena with that obtained from the glan|dular bodies. These glandular bodies are so si|tuated, that they can easily pour their liquor up|on the horns of the uterus: And I am persuaded that, during the whole season of love, there is a perpetual distillation of this liquor from the glan|dular bodies into the horns of the uterus; that this distillation continues till the glandular bodies be entirely emptied; and that they are gradual|ly effaced, leaving only behind them a small red|dish cicatrice on the external surface of the testicle.

EXPER. XXXI.

I mixed the seminal liquor of the female with an equal portion of that of the male, which was recently emitted; but the moving bodies, and every circumstance, were so entirely the same,

that I could make no distinction between those of the male and those of the female.

EXPER. XXXII.

Having dissected a young bitch that had never been in season, I discovered on one of the testi|cles only, a small solid protuberance, which I i|magined to be the rudiments of a glandular bo|dy. The surface of the testicles was smooth and uniform, and it was with difficulty I could see the lymphatic vesicles, till the membranes which cover the testicles were removed. The small quantity of liquor that was squeezed from the testicles contained no moving bodies.

EXPER. XXXIII.

In another bitch still younger, there was no appearance of glandular bodies on the testicles; their surface was white and perfectly smooth. Some small vesicles were discovered; but they seemed to contain no liquor. I compared these female testicles with those of a male of the same age, and found that their internal texture, which was fleshy, was nearly of the same nature.

EXPER. XXXIV.

I procured the uterus of a cow that had been recently killed. It was brought to me in a basket, wrapped in warm cloths, along with a live rabbit, to preserve it from cooling. The testicles were as large as a small hen's egg; on one of them was a glandular body of the size of a pea, which protruded from the testicle like a little nipple: But it had no fissure or external aperture. It was so firm and hard, that I could press no liquor out of it with my fingers. Be|fore cutting this testicle, I observed two other glandular bodies at a distance from each other. They were very small, and of a whitish yellow colour; but the large one, which seemed to have pierced the membrane of the testicle, was as red as a rose. I examined this last with great atten|tion; but could discover no liquor; from which I concluded, that it was still far from being mature.

EXPER. XXXV.

In the other testicle, there were no glandular bodies which had yet pierced the membrane that covers the testicle. Two small ones only began to appear under the membrane. I opened them both; but procured no liquor from them. They were hard bodies, with a tincture of yellow.

On each testicle there were four or five lymphatic vesicles; they were full of liquor. When ex|amined with the microscope, some small globules appeared; but there was not in them the least vestige of motion. I observed this liquor, from time to time, for two days, without discovering any thing new.

EXPER. XXXVI.

I had two other uteri conveyed to me in the same manner. The one belonged to a young cow that had never brought forth; the other to a cow which, though not old, had had several young. I first examined the testicles of the latter, and found, upon one of them, a glandu|lar body as large as a cherry. I perceived three holes into which bristles might be introduced. Having pressed the body with my fingers, a small quantity of liquor issued out, which I ex|amined, and had the pleasure of seeing moving bodies, [Pl. IV. fig. 22.], but different from what I had observed in other seminal fluids. These globules were small and obscure: Their pro|gressive motion, though distinct, was very slow. The liquor was not thick: The moving globules had no appearance of threads or tails, and they were not all in motion. These are all the ob|servations I could make on this liquor; for, though I again squeezed the glandular body, I

could not obtain any more liquor that was un|mixed with blood. The moving bodies were at least a fourth part less than the globules of the blood.

EXPER. XXXVII.

This glandular body was situated at one extremity of the testicle, near the horn of the uterus; and the liquor which it distilled must have fallen upon that horn: But, af|ter opening the horn, I found no liquor. I then opened the testicle longitudinally, and, though its cavity was considerable, it contained no fluid. At some distance from the large glan|dular body, there was a small one of the same kind, about the size of a lentil. Two cicatrices, or little pits, also appeared; they were of a deep red colour, and were the relicts of old glandu|lar bodies which had been obliterated. Having next examined the other testicle of the same cow, I discovered four cicatrices and three glan|dular bodies, the most advanced of which was of a red flesh-colour, and exceeded not the size of a pea. It was solid, without any aperture, and contained no liquor. The other two were much smaller and harder; and their colour was a kind of orange. The lymphatic vesicles were full of a clear liquid; but nothing living appear|ed in it.

EXPER. XXXVIII.

I then inspected the testicles of the young cow, which had never brought forth. They were rather larger than those of the other cow. But, what is not less remarkable than true, there was not a single cicatrice on either of them. A number of lymphatic vesicles appeared on one of the testicles; but there was no vestige of glan|dular bodies. Upon the other testicle, I could discern the rudiments of two glandular bodies, one just beginning to spring up, the other as large as a small pea. There were also many vesicles, which appeared, after being pierced with a lancet, to contain nothing. The glan|dular bodies, when opened, gave forth nothing but blood.

EXPER. XXXIX.

I cut each testicle of both cows into four parts, and, having put them into separate vials, I pour|ed as much water upon them as was just suffi|cient to cover them; and, after corking the vials close, I allowed them to infuse for six days. I then examined the infusions with the micro|scope, and saw an amazing number of moving globules, [Pl. IV. fig. 23.]. In all the infusions, the globules were extremely small, but very

active, moving with rapidity round their centres, and in all directions. I observed them, from time to time, during three days, and they always became smaller and smaller, till they totally dis|appeared on the third day.

EXPER. XL.

I procured the uteri of three other cows; and I first searched the testicles, in order to discover if there were any mature glandular bodies. In two of the uteri I found only small glandular bodies on the testicles. I was not informed whether the cows had ever brought forth; but it is probable that they had often been in season; for a number of cicatrices appeared on their te|sticles. On one of the testicles of the third cow, I observed a glandular body as large as a cherry, and very red; it was much swelled, and seemed to be perfectly ripe. I pressed the nipple, which was perforated by a hole, with my fingers, and a considerable quantity of liquor issued out. In this liquor, I found moving bodies [Pl. IV. fig. 24.] perfectly similar to those described in Exper. XXXVI. Their number was indeed greater, and their progressive motion was quick|er; they seemed to be somewhat longer; and, having observed them a long time, I perceived that they grew longer, and changed their figure. I then introduced a fine probe into the small

aperture of the glandular body; and, having cut along the probe as a directory, I found that the cavity was filled with a liquid matter. This liquor, when examined with the microscope, presented the same phaenomena, the same mo|ving bodies as in Exper. XXXVI. But I could discover in none of them either filaments or tails. The liquor of the vesicles was still transparent, and contained nothing like life or motion.

EXPER. XLI.

The uteri of several other cows were brought me at different times. In the testicles of some of them, there were glandular bodies almost ripe; in those of others, they were in different states of growth; and I perceived nothing new or uncommon, excepting that I discovered, in the testicles of two of them, glandular bodies in a decayed state, the base of one of which was as large as the circumference of a cherry. The ex|tremity of the nipple was soft and withered: The two small holes through which the fluid had issued were still visible. I introduced a small bristle into them; but there was no liquor either in the canal, or in the internal cavity, which could still be distinguished. The extinction of the glandular bodies, therefore, commences at the most external part, or extremity of the nipple. They first diminish in height, and then

[figure]

Plate VI.

in breadth, as I had an oportunity of observing in another testicle, where there was a glandular body diminished about three fourths.

EXPER. XLII.

As the testicles of female rabbits, as well as their glandular bodies, are very minute, I could make no exact experiments on their seminal li|quor. I only discovered, that the testicles of different females are in different states; and that I never saw any of them which exactly resembled De Graaf's figures.

EXPER. XLIII.

On the testicles of some cows, I found a species of bladders or vesicles, which are called hydatides by anatomists. I observed some of them large and others small; and they were at|tached to the testicle by a kind of pedicle. I examined the liquor they contained; but it was transparent, homogeneous, and every way simi|lar to the liquor in the vesicles. It had no glo|bular or moving particles.

EXPER. XLIV.

At this time, I made some experiments upon oister-water, upon water in which pepper had

been boiled, upon water in which pepper had been simply infused, and upon water in which pink-seeds were infused. The bottles contain|ing all these infusions were exactly corked. At the end of two days, I saw, in the oister-water, a vast quantity of oval and globular bodies, which seemed to swim like fishes in a pond, and had every appearance of being real animals. They had no members that could be discovered, and no tails. They were transparent, and pretty large; I saw them change their figures; they became gradually smaller and smaller during the seven or eight days that they subsisted; and, lastly, along with Mr Needham, I saw animal|cules so very similar, in an infusion of the jelly of roasted veal, which had likewise been close corked, that I am persuaded they are not true animals, agreeable to the common acceptation of that term, as shall afterwards be fully ex|plained.

The infusion of pink-seeds was crowded with innumerable moving globules, which appeared to be equally animated with those in the seminal liquors and in infusions of the flesh of animals. At first they were pretty large, and moved with great rapidity in every possible direction. They continued in this state during three weeks, and gradually diminished in size till their minuteness rendered them invisible.

The same phaenomenon took place in the in|fusions of pepper; but the moving bodies did

not appear so early as in the other infusions, and their appearance was later in the infusion of pep|per that was not boiled. I then began to suspect that what is called fermentation, might be ow|ing to the motion of these organic particles in animal and vegetable substances. To discover if there was any similarity between this species of fermentation, and that excited by mineral sub|stances, I applied to the microscope a little lime|stone powder, and poured upon it a drop of aquafortis. But the phaenomena were totally different. Large bubbles rose to the surface, and instantly darkened the lens of the microscope; when the gross parts were dissolved, every thing remained at rest, and nothing appeared which had the smallest analogy to what we perceive in the infusions of animal or vegetable bodies.

EXPER. XLV.

I examined the seminal liquor in the milts of different fishes, extracted while the animals were alive, and I observed a vast quantity of obscure moving globules. I then squeezed with my fingers the aperture in the bellies of fishes through which they emit this liquor, and, in the drops which I procured, I saw great multitudes of the same moving globules, which were almost black, and very small.

EXPER. XLVI.

Before I conclude this chapter, I shall relate the experiments of Mr Needham upon the se|men of a species of cuttle-fish, called the Calmar. This acute observer, having examined the sper|matic animals in the milts of different fishes, found them of an uncommon magnitude in the milt of the calmar. To the naked eye, they were from three to four lines in length. During a whole summer, while he dissected calmars at Lisbon, he could find no appearance of a milt, or of any reservoir destined to receive the semi|nal liquor of that fish; and it was the middle of December before he could perceive the first ve|stiges of a new vessel filled with a milty juice. This reservoir, and the juice it contained, gra|dually increased. In examining this seminal li|quor with the microscope, he saw nothing in it but small opaque globules swimming in a kind of serous matter, without any appearance of life. But, some time after, he discovered, in the milt of another calmar, organic bodies compleatly formed, which resembled spiral springs, [a, b, Pl. I. fig. 5.] inclosed in a transparent case. These springs were equally perfect at the first observation as afterwards; only they, in time, contracted themselves, and formed a kind of screw. The head of the case is a species of valve

which opens outward, and through which every thing within may be forced out. It contains, besides, another valve b, a little barrel, c, and a spongy substance d, e. Thus the whole machine consists of an outer, transparent, cartilaginous case, a, fig. 2. the superior extremity of which is terminated by a round head, formed by the case itself, and performs the office of a valve. This external case contains a transparent tube, which includes the spring, a piston or valve, a little barrel, and a spongy substance. The skrew occupies the superior part of the tube and case, the piston and barrel are situated in the middle, and the spongy substance occupies the inferior part. These machines pump the liquor of the milt; the spongy substance is full of this liquor; and, before the animal spawns, the whole milt is only a congeries of these organic bodies, which have absolutely pumped up and dried the mil|ty liquor. Whenever these small machines are taken from the body of the animal, and put a|mong water, or exposed to the air, they begin to act [Pl. V. fig. 2. and 3.]; the spring mounts up, and is followed by the piston, the barrel, and the spongy substance which contains the liquor: And, as soon as the spring and the tube in which it is contained begin to issue out of the case, the spring plaits, and the whole internal apparatus moves, till the spring, the piston, and the barrel have entirely escaped from the case. When this is effected, all the rest instantly follow, and

the milty liquor, which had been pumped, and was confined in the spongy substance, runs out through the barrel.

As this phaenomenon is extremely singular, and incontestibly proves that the moving bodies in the milt of the calmar are not real animals, but simple machines, a species of pumps, I shall here transcribe Mr Needham's own account of the matter:

'When the small machines* 1.33,' says he, 'have come to their full maturity, several of them act as soon as they are exposed to the air. Most of them, however, may be commodiously viewed by the microscope before their action commences; and, even before they act, it is necessary to moisten with a drop of water the superior extremity of the external case, which then begins to expand, while the two slender ligaments that issue out of the case are twisted and contorted in different ways. At the same time, the screw rises slowly, and the spirals at its superior end approach each other, and act against the top of the case, those which are lower seeming to be continually followed by others that issue from the piston; I say, that they seem to follow; because I believe it to be only a deception produced by the motion of the screw. The piston and barrel likewise move in the same direction; and the inferior

part, which contains the semen, extends in length, and, at the same time, moves towards the top of the case, which is apparent by the vacuity left at the bottom. As soon as the screw, with the tube in which it is inclosed, begins to appear out of the case, it twists, be|cause it is constrained by the two ligaments. The whole internal apparatus continues to move gradually and slowly till the screw, the piston, and the barrel, have entirely escaped. When that happens, the remainder issues in|stantaneously. The piston, b [Pl. V. fig. 2.]. separates from the barrel a; the ligament, which is under the barrel, swells and acquires a diameter equal to that of the spongy part which succeeds it: This, though much broader than when in the case, becomes also five times longer than formerly. The tube, which in|cluded the whole, contracts in the middle, and forms two knots or joints, d, e, [Pl. V. fig. 2. and 3.], distant about one third of its length from each extremity. Then the semen escapes by the barrel e, [fig. 2.]. It is composed of small opaque globules, which swim in a serous matter, without discovering any signs of life, and are precisely the same as I perceived them to be when diffused through the reservoir of the milt. In the figure, the part comprehend|ed between the two joints d, e, appear to be fringed. When examined attentively, this appearance seems to be occasioned by the spon|gy

substance within the tube being broken and divided into portions nearly equal. The fol|lowing phaenomena will clearly prove that this is the case.'

'It sometimes happens, that the screw and the tube break precisely above the piston b, which remains in the barrel e, [fig. 3.]. Then the tube instantly shuts; and, by contracting, assumes a conical figure above the extremity of the screw, f. This is a demonstration that it is there very elastic; and the manner in which it accommodates its figure to that of the sub|stance which includes it, when the latter un|dergoes the smallest change, proves that it is every where equally elastic.'

M. Needham hence concludes, that it is na|tural to imagine that the total action of this machine is occasioned by the spring of the screw. But, unfortunately, he proves, by several expe|riments, that the screw is acted upon by a power residing in the spongy part: As soon as the screw is separated from the rest of the machine, it ceases to act, and loses all motion. The au|thor draws the following conclusion from this singular phaenomenon.

'If I had seen,' says he, 'these pretended ani|malcules in the semen of living animals, I should, perhaps, have been able to ascertain whether they are really animated beings, or only pro|digiously small machines, which correspond in miniature to the larger vessels of the calmar.'

[figure]

Plate VII.

From this and other analogies, Mr Needham concludes, that the spermatic worms of other animals, it is reasonable to think, are only or|ganic bodies; a species of machines similar to those of the calmar, which act at different times; for, says he, if we suppose that, of the prodi|gious number of spermatic animalcules which appear in the field of the microscope, only a few thousands act at a time, this will be sufficient to make us believe the whole to be alive. If it be farther supposed, he adds, that the motion of each animalcule lasts, like that of the calmar machines, about half a minute; in this case, the successive action of the small machines would continue for a considerable time, and the ani|malcules would die one after another. Besides, why should the semen of the calmar alone con|tain machines, while that of all other animals contain real living animalcules? Here the ana|logy is so strong as to be almost irresistible. Mr Needham farther remarks, that even Leeuwen|hoek's experiments seem to indicate that the spermatic animals have a great resemblance to the organic bodies in the semen of the calmar. Speaking of the semen of the cod, Leeuwen|hoek remarks, that he imagined the oval bodies to be animalcules burst and distended, because they were four times larger than when alive. And, in another place, he observes of the semen of the dog, that the animalcules often changed

their figure, especially when the liquor began to evaporate* 1.34.

On all these accounts, Mr Needham conjec|tured, that the pretended spermatic animals were only a kind of natural machines, bodies much more simply organized than those of real ani|mals. I examined the machines of the calmar along with him, and the reader may be assured that his description of them is both exact and faithful. His experiments, therefore, demon|strate, that the seminal fluid consists of particles in quest of organization; that, in fact, it pro|duces organized bodies; but that these bodies are not animals, nor similar to the individual which produces them. It is, indeed, probable, that these organized bodies are only a kind of instru|ments for perfecting the semen, and bestowing on it an active force; and that it is by their in|ternal action that they intimately penetrate the seminal fluid of the female.

CHAP. VII.

Comparison of my own Experiments with those of Leeuwenhoek.

THOUGH my experiments were made with all the attention of which I was ca|pable, and though I often repeated them, I am satisfied that many things must have escaped me. I have only described what I saw, and what e|very man may see, at the expence of a little art and patience. To free myself from prejudice, I even attempted to forget what other observers pretended to have seen, endeavouring, by this means, to be certain of seeing nothing but what really appeared; and it was not till I had di|gested my experiments, that I wished to compare them with those of former writers, and particu|larly with those of Leeuwenhoek, who had oc|cupied himself more than 60 years in experi|ments of this kind.

Whatever authority may be due to this acute observer, it is certainly allowable to institute a comparison between a man's own observations, and those of the most respectable writer on the same subject. By an examination of this kind,

truth may be established, and errors may be de|tected, especially when the only object of in|quiry is to ascertain the genuine nature of those moving bodies which appear in the seminal fluids of all animals.

In the month of November 1677, Leeuwen|hoek, who had formerly communicated many microscopic observations to the Royal Society of London, concerning the juices of plants, the texture of trees, the optic nerve, rain-water, &c. writes to Lord Brouncker, president of the So|ciety, in the following terms: 'Postquam* 1.35 Exc. Dominus Professor Cranen me visitatione sua saepius honorarat, litteris rogavis Domino Ham cognato suo, quasdam observationum mearum videndas darem. Hic Dominus Ham me se|cundo invisens, secum in laguncula vitrea semen viri, gonorrhoea laborantis, sponte destillatum, attulit, dicens, se post paucissimas temporis mi|nutias (cum materia illa jam in tantum esset resoluta ut fistulae vitreae immitti posset) ani|malcula viva in eo observasse, quae caudam et ultra 24 horas non viventia judicabat: Idem referebat se animalcula observasse mortua post sumptam ab aegroto therebintinam. Materi|am praedicatam fistulae vitreae immissam, prae|sente Domino Ham, observavi, quasdamque in ea creaturas viventes, ac post decursum 2 aut 3 horarum eamdem solus materiam observans, mortuas vidi.'

'Eamdem materiam (semen virile) non ae|groti alicujus, non diuturna conservatione cor|ruptam, vel post aliquot momenta fluidiorem factam, sed sani viri statim post ejectionem, ne interlabentibus quidem sex arteriae pulsibus, saepiuscule observavi, tantamque in ea viven|tium animalculorum multitudinem vidi, ut in|terdum plura quam 1000 in magnitudine a|renae sese moverent; non in toto semine, sed in materia fluida crassiori adhaerente, ingen|tem illam animalculorum multitudinem obser|vavi; in crassiori vero seminis materia quasi sine motu jacebant, quod inde provenire mihi imaginabar, quod materia illa crassa ex tam va|riis cohaereat partibus, ut animalcula in ea se movere nequirent; minora globulis sanguini ruborem adferentibus haec animalcula erant, ut judicem, millena millia arenam grandiorem magnitudine non aequatura. Corpora corum rotunda, anteriora obtusa, posteriora ferme in aculeum desinentia habebant; cauda tenui lon|gitudine corpus quinquies sexiesve excedente, et pellucida, crassitiem vero ad 25 partem cor|poris habente, praedita erant, adeo ut ea quo ad figuram cum cyclaminis minoribus, longam caudam habentibus, optime comparare queam: Motu caudae serpentino, aut ut anguillae in aqua natantis, progrediebantur; in materia vero aliquantulum crassiori caudam octies deciesve quidem evibrabant antequam latitudinem capilli procedebant. Interdum imaginabar me inter|noscere

noscere posse adhuc varias in corpore horum animalculorum partes, quia vero continuo eas videre nequibam, de iis tacebo. His animal|culis minora adhuc animalcula, quibus non nisi globuli figuram attribuere possum, permista erant.'

'Memini me ante tres aut quatuor annos, ro|gatu Domini Oldenburg B. M. semen virile ob|servasse, et praedicta animalia pro globulis ha|buisse; sed quia fastidiebam ab ulteriori inqui|sitione, et magis quidem a descriptione, tunc temporis eam omisi. Jam quoad partes ipsas, ex quibus crassam seminis materiam, quoad majorem sui partem consistere saepius cum ad|miratione observavi, ea sunt tam varia ac multa vasa, imo in tanta multitudine haec vasa vidi, ut credam me in unica seminis gutta plura ob|servasse quam anatomico per integrum diem subjectum aliquod secanti occurrant. Quibus visis, firmiter credebam nulla in corpore hu|mano jam formato esse vasa, quae in semine virili bene constituto non reperiantur. Cum materia haec per momenta quaedam aëri fuisset exposita, praedicta vasorum multitudo in aquo|sam magnis oleaginosis globulis permistam ma|teriam mutabatur,' &c.

The secretary of the Royal Society replied to this letter of Leeuwenhoek, that it would be proper to make similar experiments on the semi|nal fluids of other animals, not only to support the original discovery, but to distinguish what|ever differences might appear in the number and

figure of the animalcules: And, with regard to the vascular texture of the thick part of the se|minal fluid, he suspected that it was only a con|geries of filaments, without any regular organi|zation: 'Quae tibi videbatur vasorum congeries, fortassis seminis sunt quaedam filamenta, haud organice constructa, sed dum permearunt vasa generationi inservientia in istiusmodi figuram elongata. Non dissimili modo ac saepius no|tatus sum salivam crassiorem ex glandularum faucium foraminibus editam, quasi e convolutis fibrillis constantem* 1.36.'

Leeuwenhoek replied, 18th March 1678, in the following words: 'Si quando canes coeunt marem a foemina statim seponas, materia quae|dam tenuis et aquosa (lympha scilicet sperma|tica) a pene solet paulatim exstillare; hanc ma|teriam numerosissimis animalculis repletam ali|quoties vidi, eorum magnitudine quae in se|mine virili conspiciuntur, quibus particulae globulares aliquot quinquagies majores per|miscebantur.'

'Quod ad vasorum in crassiori seminis virilis portione spectabilium observationem attinet, denuo non semel iteratam, saltem mihimetipsi comprobasse videor; meque omnino persuasum habeo, cuniculi, canis, felis, arterias venasve fuisse a peritissimo anatomico haud unquam magis perspicue observatas, quam mihi vasa in semini virili, ope perspicilli, in conspectum venere.'

'Cum mihi praedicta vasa primum innotuere, statim etiam pituitam, tum et salivam perspi|cillo applicavi; verum hic minime existentia animalia frustra quaesivi.'

'A cuniculorum coitu lymphae spermaticae guttulam unam et alteram, e femella extillan|tem, examini subjeci, ubi animalia praedicto|rum similia, sed longe pauciora, comparuere. Globuli item quam plurimi, plerique magnitu|dine animalium, iisdem permisti sunt.'

'Horum animalium aliquot etiam delinea|tiones transmisi; figura 1. [pl. VI. fig. 1.] ex|primit eorum aliquot vivum (in semine cuni|culi arbitror) eaque forma qua videbatur, dum aspicientem me versus tendit. A B C, capitu|lum cum trunco indicant; C D, ejusdem cau|dam, quam pariter ut suam anguilla inter na|tandum vibrat. Horum millena millia, quan|tum conjectare est, arenulae majoris molem vix superant. [Pl. VI. fig. 2. 3. 4.] sunt ejusdem generis animalia, sed jam emortua.'

'[Pl. VI. fig. 5.] delineatur vivum animalcu|lum quemadmodum in semine canino sese ali|quoties mihi attentius intuenti exhibuit. E F G, caput cum trunco indigitant, G H, ejusdem caudam. [Pl. VI. fig. 6. 7. 8.] alia sunt in semine canino quae motu et vita privantur, qualium etiam vivorum numerum adeo in|gentem vidi, ut judicarem portionem lymphae spermaticae arenulae mediocri respondentem, eorum ut minimum decena millia continere.'

In another letter to the Royal Society, dated May 31. 1678, Leeuwenhoek adds, 'Seminis canini tantillum microscopio applicatum iterum contemplatus sum, in eoque antea descripta animalia numerosissime conspexi. Aqua plu|vialis pari quantitate adjecta, iisdem confestim mortem accercit. Ejusdem seminis canini por|tiuncula in vitreo tubulo unciae partem duo|decimalem crasso servata, sex et triginta hora|rum spatio contenta animalia vita destituta ple|raque, reliqua moribunda videbantur.'

'Quo de vasorum in semine genitali existen|tia magis constaret, delineationem aliqualem mitto, ut in figura A B C D E [pl. VI. fig. 9.] quibus literis circumscriptum spatium arenu|lam mediocrem vix superat.'

I have transcribed these passages from the Phi|losophical Transactions, because they first ap|peared in that work, before Leeuwenhoek had formed any theory; and, therefore, they must be more agreeable to truth. After the ingenious author had formed a system of generation, his account of the spermatic animals varies, even in matters that are essential* 1.37.

In the first place, what he says concerning the number of these pretended animalcules is true; but the figure of their bodies corresponds not always to his description. Sometimes the end next the tail is globular and sometimes cylindri|cal;

sometimes it is flat, and at other times it is broader than long, &c. With regard to the tail, it is often thicker and shorter than he makes it. The vibratory motion, he a|scribes to the tail, and by which he alledges the animals are enabled to proceed forward, I never could distinguish in the manner he de|scribes it. I have seen these moving bodies vi|brate eight or ten times, from right to left, or from left to right, without advancing the breadth of a single hair; and I have observed many of them which never could proceed forward, because this tail, in place of assisting them to swim, was, on the contrary, a small thread attached to the fila|ments or mucilaginous part of the liquor, and, of course, totally prevented the progressive mo|tion of the body. Even when the tail appeared to have any motion, it only resembled the small bendings of a thread at the end of a vibration. I have seen these threads or tails fixed to the filaments, which Leeuwenhoek calls vessels: I have seen them separate from the fila|ments, after repeated efforts made by the moving bodies; I have seen them first long, then dimi|nish, and at last disappear. Thus these tails ought to be regarded as accidental appendages, and not as real members of the moving bodies. But, what is more remarkable, Leeuwenhoek expressly affirms, in this letter to Lord Brouncker, that, besides the tailed animals, he observed in this liquor animalcules still more minute that had no tails, and were perfectly globular: 'His

[figure]

Plate VIII.

animalculis (caudatis scilicet) minora adhuc animalcula, quibus non nisi globuli siguram attribuere possum, permista erant.' This is the truth. After Leeuwenhoek, however, had main|tained that these animalcules were the only effi|cient principle of generation, and that they were transformed into men, he regards as real animals only those which had tails; and, accordingly, as it was necessary that animalcules, to be trans|formed into men, should have a constant and in|variable figure, he never afterwards mentions the round animals without tails. I was struck with the difference between the original compo|sition of this letter, and the form in which it ap|peared twenty years afterwards in his third vo|lume: For, instead of the words which we have just now quoted, we meet with the following in pag. 63. 'Animalculis hisce permistae jacebant aliae minutiores particulae, quibus non aliam quam globulorum seu sphaericam figuram as|signare queo.' This is a very different account of the matter. A particle of matter, to which he ascribes no motion, is extremely different from an animalcule. It is astonishing that Leeuwen|hoek, in copying his own letter, should have changed an article of so much consequence. What he immediately subjoins likewise merits attention. He says, that, at the intreaty of Mr Oldenburg, he had examined this liquor three or four years ago; and that he then imagined these animalcules to be globules. Thus, these

pretended animalcules are sometimes globules without any sensible motion; sometimes they are globules which move with great activity; some|times they have tails, and sometimes no tails. Speaking of spermatic animals in general, he re|marks * 1.38, 'Ex hisce meis observationibus cogitare coepi, quamvis antehac, de animalculis in semi|nibus masculinis agens, scripserim me in illis caudas non detexisse, fieri tamen posse ut illa animalcula aeque caudis fuerint instructa, ac nunc comperi de animalculis in gallorum gal|linaccorum semine masculino:' Another proof that he has often seen spermatic animals of all kinds, without tails.

Secondly, It is worthy of remark, that Leeu|wenhoek had very early discovered the filaments which appear in the semen before it be liqui|sied; and that, at that time, when he had not framed his hypothesis concerning the spermatic animals, he conceived the filaments to be veins, nerves, and arteries. He firmly believed, that all the parts and vessels of the human body might be clearly distinguished in the seminal fluid. He even persisted in this opinion, not|withstanding the representations made to him by Mr Oldenburg, in name of the Royal Society. But, after he conceived the notion of transform|ing his spermatic animals into men, he never again takes any notice of these vessels. Instead of regarding them as the nerves and blood-ves|sels

of the human body already formed in the semen, he does not even ascribe to them their real function, which is the production of the moving bodies. He observes* 1.39, 'Quid fiet de omnibus illis particulis seu corpusculis praeter illa animalcula semini virili hominum inhae|rentibus! Olim et priusquam haec scriberem, in ea sententia fui praedictas strias vel vasa ex testiculis principlum secum ducere,' &c. And, in another place, he says, that what he had for|merly remarked concerning vessels in the semen deserved no attention.

Thirdly, If we compare the figures 1. 2. 3. and 4. Pl. VI. and VII. which we have represented exactly as they appear in the Philosophical Transactions, with those which Leeuwenhoek caused to be engraved several years after, we shall find very great differences, especially in those of the dead animalcules of the rabbit, 1. 3. and 4. and in those of the dog, which I have also delineated, in order to give a distinct idea of the matter. From all this, it may fairly be concluded, that Leeuwenhoek has not always seen the same phaenomena; that the moving bodies, which he regards as animals, have appeared to him under different forms; and that he has contradicted himself with a view to make the species of men and of animals uniform and consistent. He not only varies as to the fundamental part of these experiments, but also as to the manner of ma|king

them; for he expressly tells us, that he al|ways diluted the semen with water, to separate its parts, and to give more freedom of motion to the animalcules* 1.40; and yet, in his first letter to Lord Brouncker, he says, that, when he mixed the semen of dogs, in which he before had seen innumerable animals, with water, they all in|stantly died. Thus Leeuwenhoek's first experi|ments were made, like mine, without any mix|ture; and, it appears, that he was not in use to mix the liquor with water till long after he be|gan his experiments, and till he conceived the idea of water's killing the animalcules; which, however, is not true: I imagine that the addi|tion of water only dissolves the filaments too suddenly; for, in all my experiments, I have seen but very few filaments in the liquor, after its being mixed with water.

Leeuwenhoek was no sooner persuaded that the spermatic animalcules were transformed in|to men and other animals, than he imagined that he saw two distinct kinds in the semen of every animal, the one male, and the other female. Without this difference of sex in the spermatic animalcules, it was difficult, he says, to conceive the possibility of producing males and females by simple transformation. He mentions these male and female animalcules in his letter published in the Philosophical Transactions, No. 145. and in several other places* 1.41. But he attempts not to

describe the differences between male and fe|male animalcules, which never existed but in his own imagination.

The famous Boerhaave having asked Leeu|wenhoek, whether he had observed any diffe|rences in the growth and size of spermatic ani|mals? Leeuwenhoek replied, that, in the semen of a rabbit which he had opened, he saw an in|finite number of animalcules: 'Incredibilem,' says he, 'viventium animalculorum numerum conspexerunt, cum haec animalcula scypho imposita vitreo et illic emortua, in rariores or|dines disparassent, et per continuos aliquot dies saepius visu examinassem, quaedam ad justam magnitudinem nondum excrevisse adverti. Ad haec quasdam observavi particulas perexiles et oblongas, alias aliis majores, et, quantum ocu|lis apparebat, cauda destitutas; quas quidem particulas non nisi animalcula esse credidi, quae ad justam magnitudinem non excrevissent* 1.42.' Here we have animalcules of different sizes, and some with tails, and others that had no tails, which better corresponds with my experiments than with Leeuwenhoek's system. We only differ in a single article. He considers the oblong bodies without tails as young animalcules which have not yet arrived at their full growth: But I, on the contrary, have seen these pretended ani|mals originally spring from the filaments with their tails or threads, which they gradually lost.

In the same letter to Boerhaave he says* 1.43, that, in the semen of a ram he observed the animal|cules marching in flocks like sheep: 'A tribus circiter annis testes arietis, adhuc calentes, ad aedes meas deferri curaveram; cum igitur ma|teriam ex epididymibus eductam, ope micro|scopii contemplarer, non sine ingenti voluptate advertebam animalcula omnia, quotquot inna|tabant semini masculino, eundem natando cur|sum tenere, ita nimirum ut quo itinere priora praenatarent, eodem posteriora subsequerentur, adeo ut hisce animalculis quasi sit ingenitum, quod oves factitare videmus, scilicet ut praece|dentium vestigiis grex universus incedat.' This observation, made by Leeuwenhoek in the 1713, and which he regarded as new and singular, is a sufficient proof that he had never so attentively examined the seminal fluids of animals as to en|able him to give exact descriptions of them. In the 1713, he was 71 years of age: He had been in the constant practice of making experiments with the microscope for 45 years: He continu|ed to publish his observations during 36 years: And yet, after all this practice, he now, for the first time, observed a phaenomenon which is ex|hibited in every semen, and which I have de|scribed, Exper. IX. in the human semen, Ex|per. XII. in the semen of a dog, and Exper. XXIX in the semen of a bitch. To explain the moving of the animalcules of the ram in flocks,

[figure]

Plate IX.

therefore, it is unnecessary to suppose them en|dowed with the natural instinct peculiar to sheep; since those of man, of the dog, and of the bitch, move in the very same manner; and since this motion depends upon particular circumstances, the principal of which is, that the fluid part of the semen should be on one side, and the thick or filamentous part on the other; for then the whole moving bodies disengage themselves from the filaments, and proceed, in the same direction, into the more fluid part of the liquor.

In another letter, written the same year, and addressed to Boerhaave* 1.44, he relates some farther observations concerning the semen of the ram: He tells us, that, when the liquor was put into separate glasses and examined, he observed flocks of animalcules moving all in the same direction, and other flocks returning the contrary way. He adds: 'Neque illud in unica epididymum parte, sed et in aliis quas praecideram partibus, observavi. Ad haec, in quadam parastatarum resecta portione complura vidi animalcula, quae necdum in justam magnitudinem adoleverant; nam et corpuscula illis exiliora et caudae triplo breviores erant quam adultis. Ad haec, caudas non habebant desinentes in mucronem, quales tamen adultis esse passim comperio. Practerea, in quandam parastatarum portionem incidi, a|nimalculis, quantum discernere potui, destitu|tam, tantum illi quaedam perexiguae inerant

particulae, partim longiores partim breviores; sed altera sui extremitate crassiunculae; istas particulas in animalcula transituras esse non du|bitabam.' From this passage, it is apparent that Leeuwenhoek had seen in this seminal liquor, what I have found in the semen of all the ani|mals which I examined, moving bodies that differ|ed in size, figure, and motion; and these cir|cumstances, it is obvious, correspond better with the notion of organic particles in motion, than with that of real animals.

It appears, therefore, that Leeuwenhoek's ob|servations, though he draws very different con|clusions from them, perfectly correspond with mine: And, though there be some opposition in the facts, I am fully persuaded, that, whoever shall take the trouble of repeating the experiments, will easily discover the source of these diffe|rences, and find that I have related nothing but truth. To enable the reader to decide in this matter, I shall add a few remarks.

We do not always see, in the human semen, the filaments I have mentioned: For this pur|pose, the liquor must be examined the moment it is extracted from the body; and even then they do not uniformly appear. When the li|quor is too thick, it presents nothing but large globules, which may be distinguished with a common lens. When examined with the mi|croscope they have the appearance of small oran|ges; they are very opaque, and one of them oc|cupies

the whole field of the microscope. The first time I observed these globules, I imagined them to be foreign bodies which had fallen into the liquor. But, after examining different drops, I found that the whole liquor was composed of these large globules. I observed one of the largest and roundest of them for a long time. At first it was perfectly opaque: A little after, I perceived on its surface, about half way be|tween the centre and circumference, a beautiful coloured luminous ring, which continued more than half an hour, then gradually approached the centre, which became clear and coloured, while the rest of the globule remained opaque. This light which illuminated the centre, resem|bled that which appears in large air-bubbles. The globule now began to grow flat, and to have a small degree of transparency: And, after observing it for three hours, I could perceive no other change, no appearance of motion, either internal or external. I imagined that some change might happen by mixing the liquor with water. The globules were indeed changed into a trans|parent homogeneous fluid, which presented no|thing worthy of remark. I left the semen to liquify of its own accord, and examined it at the distance of 6, 12, and 24 hours; but found no|thing like life or motion. I relate this experi|ment to show, that the ordinary phaenomena are not always to be expected in seminal fluids, though they be apparently similar.

Sometimes all the moving bodies have tails, especially in the semen of man, and of the dog; their motion is not then very rapid, and appears to be performed with difficulty. If the liquor be allowed to dry, the tails or threads are first deprived of motion; the anterior extremity con|tinues to vibrate for some time, and then all mo|tion ceases. These bodies may be long preserved in this state; and, if a small drop of water be then poured upon them, their figure changes; they fall down into several minute globules, which appear to have a small degree of motion, some|times approaching each other, and sometimes trembling, and turning round their centres.

The moving bodies in the human semen, and in those of the dog and bitch, resemble each o|ther so strongly, that it is not easy to distinguish them, especially when examined immediately af|ter they are taken from the body of the animal. Those of the rabbit appear to be smaller and more active. But these differences and resem|blances proceed more from the different states of the fluids during the time of examination, than from the nature of the fluids themselves, which ought indeed to be different in different species of animals: For example, in the human fluid, I have remarked large filaments, as repre|sented in Pl. 1. fig. 3. &c. and I have seen the moving bodies separate from these filaments, from which they appeared to derive their origin. But I could perceive nothing of this kind in the

semen of the dog. In place of distinct filaments, it is generally composed of a compact mucilage, in which we with difficulty perceive some fila|mentous parts; and yet this mucilage gives birth to moving bodies similar to those in the human semen.

The motion of these bodies continues longer in the fluid of the dog, than in that of man, which enables us more easily to distinguish the change of form above taken notice of. The mo|ment the fluid issues from the body of the ani|mal, we find most of the animalcules possessed of tails. In 12, 24, or 36 hours afterwards, al|most the whole tails disappear; we then per|ceive only oval bodies moving about, and gene|rally with more rapidity than at first.

The moving bodies are always below the sur|face of the liquor. Several large transparent air-bubbles commonly appear on the surface; but they have no motion, unless when the li|quor is agitated. Below the moving bodies we often perceive others still more minute: These have no tails; but most of them move: And, in general, I have remarked, that, of the number|less globules in all these liquors, the smallest are generally blacker and more obscure than the o|thers; and that those which are extremely mi|nute and transparent have little or no motion. They seem likewise to have more specific gravi|ty; for they are always sunk deepest in the fluid.

CHAP. VIII.

Reflections on the preceding Experiments.

FROM the foregoing experiments, it ap|pears, that females, as well as males, have a seminal fluid containing bodies in motion; that these moving bodies are not real animals, but only organic living particles; and that these particles exist not only in the seminal fluids of both sexes, but in the flesh of animals, and in the seeds of vegetables. To discover whether all the parts of animals and all the seeds of plants contained moving organic particles, I made in|fusions of the flesh of different animals, and of the seeds of more than twenty different species of vegetables; and, after remaining some days in close glasses, I had the pleasure of seeing organic moving particles in all of them. In some they appeared sooner, in others later. Some preser|ved their motion for months, and others soon lost it. Some, at first, produced large moving globules, resembling animals, which changed their figure, split, and became gradually smaller. Others produced only small globules whose mo|tions were extremely rapid; and others produ|ced

filaments, which grew longer, seemed to vege|tate, and then swelled, and poured out torrents of moving globules. But it is needless to give a detail of my experiments on the infusions of plants, especially since Mr Needham has publish|ed his excellent and numerous observations on this subject. To this able naturalist I have read over the preceding treatise; I have often rea|soned with him on the resemblance between the moving bodies in infusions of the seeds of vege|tables, and those in the seminal fluids of male and female animals. He thought my views well founded, and of sufficient importance to merit a farther discussion. He, therefore, began to make experiments on the different parts of vege|tables; and I acknowledge, that he has brought the ideas I communicated to greater perfection, than could have been done by me. Of this I could give many examples: But I shall confine myself to one, because I formerly pointed out the fact in question, which he describes in the following manner.

To ascertain whether the moving bodies which appear in infusions of flesh were real animals, or only, as I had imagined, organic moving par|ticles, Mr Needham thought that an examination of the jelly of roasted meat would determine the question; because, if they were animals, the fire would destroy them, and, if not, they would still be perceptible, in the same manner as when the flesh was raw. Having, for this purpose, ta|ken

the jellies of veal and of other kinds of roast|ed meat, he put them in glasses filled with water, and carefully corked the bottles. After some days infusion, he found in the whole of the liquors an immense number of moving bodies. He showed me several of these infusions, and, among others, that of the veal jelly, which contained moving bodies very similar to those of man, the dog, and the bitch, after they had lost their tails or threads. Though they changed their forms, their motions were so similar to those of animals swimming, that, whoever saw them for the first time, or had been ignorant of what has been formerly remarked concerning them, would certainly have apprehended them to be real ani|mals. I shall only add, that Mr Needham has established, by numberless experiment, the exist|ence of moving organic particles in all the parts of vegetables, which confirms what I have alledged, and extends my theory concerning the composition and reproduction of organized be|ings.

It is them apparent, that all animals, whether male or female, and every species of vegetable, are composed of living organic particles. These organic particles abound most in the seminal fluids of animals, and in the seeds of vegetables. Re|production is effected by the union of these or|ganic particles, which are detached from all parts of the animal or vegetable body, and are always similar to the particular species to which

they belong; for their union could not be ac|complished but by the intervention of an inter|nal mould, which is the efficient cause of the figure of the animal or vegetable, and in which the essence, the unity, and the continuation of the species consists, and will invariably continue till the end of time.

But, before drawing general conclusions from the system I have established, some objections must be removed, which will contribute still farther to illustrate the subject.

It will be demanded of me, why I deny these moving bodies to be animals, after they have uniformly been recognized as such by every man who has examined them? It may likewise be asked, How is it possible to conceive the na|ture of living organic particles, unless we allow them to be real animals? And to suppose an a|nimal to be composed of lesser animals, is near|ly the same idea, as when we say, that an orga|nized body is composed of organic living par|ticles. To these questions, I shall endeavour to give satisfactory answers.

It is true, that almost all observers agree in regarding the moving bodies in the seminal fluid as real animals. But it is equally certain, both from my experiments, and those of Mr Need|ham upon the semen of the calmar, that these moving bodies are beings more simple and less organized than animals.

The word animal, in its common acceptation, represents a general idea, composed of particular ideas which we derive from particular animals. All general ideas include many different ideas, which more or less approach or recede from one another; and, of course, no general idea can be precise or exact. The general idea we have formed of an animal, may be derived from the particular idea of a dog, of a horse, and of other animals, from the power of volition, which en|ables them to act according to their inclination, and from the circumstances of their being com|posed of flesh and blood, from their faculty of chusing and of taking nourishment, from their senses, from the distinction of sexes, and from their power of reproducing. The general idea, therefore, expressed by the word animal, includes a number of particular ideas, not one of which constitutes the essence of the general idea: For there are animals which have no intelligence, no will, no progressive motion, no flesh or blood, and appear to be only a mass of congealed mu|cilage: There are others, which cannot seek for their food, and only receive it from the element in which they exist; others have no senses, not even that of feeling, at least in a perceptible de|gree. Some have no sexes, or have both in one individual. There remains nothing, there|fore, in the properties of an animal, but the power of reproduction, which is common to both the vegetable and animal. It is from the

whole taken together that a general idea is formed; and, as this whole is composed of dif|ferent parts, there must of necessity be degrees or intervals between these parts. An insect, in this sense, is less an animal than a dog, an oyster than an insect, and a sea-nettle, or a fresh water polype, than an oyster: And, as Nature proceeds by insensible degrees, we should find beings par|taking of still less animation than a sea-nettle or a polype. Our general ideas are only artificial methods of collecting a number of objects un|der one point of view; and they have, like o|ther artificial methods, the defect of not being able to comprehend the whole. They are in direct opposition to the procedure of Nature, which is uniform, insensible, and always parti|cular. It is to grasp a number of particular ideas under one word, of which we have no clearer notion than that word conveys; because, when the word is once received, we imagine it to be a line drawn between the different pro|ductions of nature; that every thing above this line is an animal, and every thing below it a ve|getable, which is another word equally general, and employed as a line of separation between organized bodies and brute matter. But, as has already been remarked, these lines of separation have no existence in nature. There are bodies which are neither animals, vegetables, nor mi|nerals, and every attempt to arrange them un|der either of these classes must be ineffectual.

For example, Mr Trembly, when he first exa|mined the fresh water polypus, spent much time before he could determine whether it was an animal or a vegetable. The reason is plain; this polypus is perhaps neither the one nor the other; and all that can be said is, that it has most resemblance to an animal: And, as we are inclined to think, that every living being is ei|ther an animal or a plant, we believe not the ex|istence of any organized body, unless it falls un|der some of these general denominations, al|though there must be, and in fact there are, many beings which belong neither to the one nor the other. The moving bodies found in the seminal fluids, and in infusions of the flesh of animals, as well as in those of all parts of ve|getables, are of this species: We can neither rank them under animals nor vegetables; and no man in his senses will ever maintain them to be minerals.

We may, therefore, pronounce, without hesi|tation, that the great division of natural pro|ductions into animals, vegetables, and minerals, comprehends not all material beings; since be|ings exist which can be included in neither of these classes. Nature passes, by imperceptible steps, from the animal to the vegetable; but, from the vegetable to the mineral, the passage is sudden, and the interval great. Here the law of imperceptible degrees suffers a violation. This circumstance made me suspect, that, by exami|ning

Nature more closely, we should find inter|mediate organized beings, which, without ha|ving the faculty of reproduction, like animals and vegetables, would still enjoy a species of life and motion; beings which, without being either animals or vegetables, might enter into the con|stitution of both; and, lastly, beings which would consist of the first assemblages of the or|ganic particles mentioned in the preceding chapters.

Eggs constitute the first class of this species of beings. Those of hens and other female birds are attached to a common pedicle, and derive their nourishment and growth from the body of the animal. But, when attached to the ova|rium, they are not properly eggs; they are only yellow globes, which separate from the ova|rium as soon as they acquire a certain magnitude: Such is their internal organization, however, that they absorb nourishment from the lymph contained in the uterus, and convert it into the white, membranes, and shell. Thus the egg pos|sesses a species of life and organization. It grows and assumes a form by its own peculiar powers: It neither lives like an animal, nor vegetates like a plant, nor enjoys the faculty of reproduction. The egg, therefore, is a distinct being, which can neither be ranked with the animal nor mi|neral kingdoms. If it be alledged, that the egg is only an animal production destined for the nourishment of the chick, and ought to be re|garded

as a part of the hen; I reply, that eggs, whether impregnated or not, are always organi|zed in the same manner; that impregnation changes only a part which is almost invisible; that it grows, and acquires a uniform figure and structure, both externally and internally, inde|pendent of impregnation; and, consequently, it ought to be considered as a separate and di|stinct being.

This will be still more apparent, if we attend to the growth and formation of the eggs of fishes. When the female deposits them in the water, they are properly but the rudiments of eggs, which, being lately separated from the body of the animal, attract and assimilate those particles that are fitted for their nourishment; and thus increase in size by mere absorption. In the same manner as the egg of the hen ac|quires its white and membranes while floating in the uterus, the eggs of fishes acquire their white and membranes in the water; and, whether they are fecundated by the male's shedding his milt upon them, or they remain un|impregnated, they still arrive at full perfection. It is plain, therefore, that eggs in general ought to be regarded as organized bodies, and forming a distinct genus from animals and vegetables.

The organized bodies found in the semen of all animals, and which, like those in the milt of the calmar, are natural machines, and not ani|mals, form a second species of the same genus.

They are properly the first assemblages of those organic particles so often mentioned; and, per|haps, they are the constituent particles of all a|nimated bodies. They appear in the semen of every animals, because the semen is only the re|sidue of the organic particles which the ani|mal takes in with its food. The particles, as formerly remarked, assimilated from the food, are those which are most organized, and the most analogous to the animal itself: It is of these particles that the semen consists; and, of course, we ought not to be surprised to find or|ganized bodies in that fluid.

To be satisfied that these organized bodies are not real animals, we have only to reflect upon the preceding experiments. The moving bo|dies in the semen have been considered as real animals, because they have a progressive motion, and something similar to tails. But, after attend|ing, on the one hand, to the nature of this mo|tion, which is suddenly finished, and never again commences, and, on the other, to the nature of the tails, which are only threads adhering to the moving body, we will begin to hesitate; for an animal goes sometimes slow, and sometimes fast; and it sometimes stops, and reposes, without moving at all. These moving bodies, on the contrary, go always in the same direction at the same time; I never saw them stop and again begin to move; and, if they once stop, it is for ever. I demand, if this continued motion, with|out

any repose, is common to animals; and if, from this circumstance, we ought not to doubt concerning the real animation of these moving bodies? An animal should always have a uni|form figure, as well as distinct members: But these moving bodies change their figure every moment; they have no distinct members; and their tails are only adventitious matter, and no part of the individual. How, then, can they be esteemed real animals? In seminal liquors, we see silaments which stretch out, and seem to ve|getate; then they swell and produce moving bo|dies. These filaments are, perhaps, of a vege|table nature; but the moving bodies which proceed from them cannot be animals; for we have no example of vegetables giving birth to animals. Moving bodies are found in all animal and ve|getable substances promiscuously. They are not the produce of generation. They have no uni|formity of species. They cannot, therefore, be either animals or vegetables. As they are to be met with in every part of animals and of vege|tables, but are most abundant in their seeds, is it not natural to regard them as the organic living particles of which animals and vegetables are composed, as particles which, being endowed with motion, and a species of life, ought to produce, by their union, moving and living beings, and, in this manner, form animals and vegetables?

But, to remove every doubt upon this subject, let us attend to the observations of others. Can the active machines discovered by Mr Needham in the milt of the calmar be regarded as animals? Can we believe that eggs, which are active ma|chines of another species, are also animals? If we examine Leeuwenhoek's representations of the moving bodies found in many different sub|stances, will we not be satisfied, at the first in|spection, that they are not animals, since none of them have any members, but are uniformly either round or oval? If we attend to what this famous observer has remarked concerning the motion of these pretended animals, we must be convinced that he was wrong in regarding them as real animals, and we will be more and more confirmed in the opinion, that they are only organic moving particles. We shall give some examples. Leeuwenhoek* 1.45, gives the figure of the moving bodies in the seminal fluid of a male frog. This figure represents nothing but a thin, long body, pointed at one of the extremities. Let us attend to what he says concerning it: 'Uno tempore caput, (that is, the largest ex|tremity of the moving body), crassius mihi apparebat alio; plerumque agnoscebam ani|malculum haud ulterius quam a capite ad medium corpus, ob caudae tenuitatem, et cum idem animalculum paulo vehementius move|retur (quod tamen tarde fiebat) quasi volumine

quodam circa caput ferebatur. Corpus fere carebat motu, cauda tamen in tres quatuorve flexus volvebatur.' Here we have the change of figure that I had observed, the mucilage from which the moving bodies with difficulty disengage themselves, the slowness of their mo|tion before they escape from the mucilage, and, lastly, a part of the pretended animal in mo|tion while the other is dead; for, a little after|wards, he observes, 'movebant posteriorem so|lum partem, quae ultima, morti vicinia esse judicabam.' All this is repugnant to the na|ture of an animal, but exactly corresponds with my experiments, excepting that I never saw the tail move but in consequence of an agitation of the body. Speaking of the seminal fluid of the cod, he says* 1.46, 'Non est putandum omnia ani|malcula in semine aselli contenta uno eodem|que tempore vivere, sed illa potius tantum vi|vere quae exitui seu partui viciniora sunt, quae et copiosiori humido innatant prae reliquis vita carentibus, adhuc in crassa materia, quam hu|mor eorum efficit, jacentibus.' If these are animals, why were they not all alive? Why did those only live which were in the most fluid part of the liquor? Leeuwenhoek did not observe, that the thick part, instead of being a humor produced by the animalcules, is a mucilage which gives birth to them. If he had diluted the mucilage with water, he would at once have

given life and motion to the whole. The mu|cilage itself is often nothing else than a mass of those bodies, which begin to move as soon as they can disengage themselves; and, of course, this thick matter or mucilage, instead of being a humour produced by the animalcules, is only a congeries of the animals themselves, or rather, as formerly remarked, the matter of which they are formed. Speaking of the semen of the cock, Leeuwenhoek, in his letter to Grew, says* 1.47, 'Contemplando materiam (seminalem) animad|verti ibidem tantam abundantiam viventium animalium, ut ea stuperem; forma seu externa figura sua nostrates anguillas fluviatiles refe|rebant, vehementissima agitatione movebantur; quibus tamen substrati videbantur multi et ad|modum exiles globuli, item multae plan-ova|les figurae, quibus etiam vita posset attribui, et quidem propter carumdem commotiones; sed existimabam omnes hasce commotiones et agitationes provenire ab animalculis, sicque etiam res se habebat; attamen ego non opi|nione solum, sed etiam ad veritatem mihi per|suadeo has particulas, planam et ovalem sigu|ram habentes, esse quaedam animalcula inter se ordine suo disposita et mixta, vitaque adhuc carentia.' Here we have animalcules, in the same seminal fluid, of different forms; and I am convinced, from my own experiments, that, if Leeuwenhoek had observed those oval bodies

with attention, he would have perceived that they moved with their own proper force, and, consequently, that they were as much alive as the others. This change of figure, it is true, exactly corresponds with what I had observed: But it does not indicate a uniform species of a|nimals; for, in the present example, if the bo|dies having the figure of a serpent were genuine spermatic animalcules, each of which was destined to become a cock, and therefore implies a uni|form and invariable organization, what was the end and destination of those of an oval figure? He, indeed, afterwards remarks, that these oval bodies might be the same with the serpentine, if we suppose them rolled up in a spiral manner. But still, how is it possible to conceive that an animal, with its body in this restrained posture, should be able to move without extending itself? I, therefore, maintain, that these oval bodies were only the organic particles separated from their threads or tails, and that the serpentine bodies were the same particles which had not yet been deprived of these appendages, as I have often remarked in other seminal fluids.

Besides, Leeuwenhoek, who believed all these moving bodies to be real animals, who establish|ed a system upon that foundation, and who af|firmed, that spermatic animalcules were trans|formed into men and other animals, now suspec|ted them to be only natural machines, or moving organic particles. He never entertained a doubt,

but that these animalcules contained the large animal in miniature. He remarks* 1.48, 'Progene|ratio animalis ex animalculo in seminibus mas|culinis omni exceptione major est; nam, etiamsi in animalculo ex semine masculo, unde ortum est, figuram animalis conspicere nequeamus, attamen satis superque certi esse possumus figuram animalis ex qua animal ortum est, in animalculo quod in semine masculo re|peritur, conclusam jacere sive esse: Et quan|quam mihi saepius, conspectis animalculis in semine masculo animalis, imaginatus fue|rim me posse dicere, en ibi caput, en ibi humeros, en ibi femora; attamen cum ne mi|nima quidem certitudine de iis judicium ferre potuerim, hucusque certi quid statuere super|sedeo, donec tale animal, cujus semina mascula tam magna erunt, ut in iis figuram creaturae ex qua provenit agnoscere queam, invenire secunda nobis concedat fortuna.' This op|portunity, so much desired by Leeuwenhoek, happily occurred to Mr Needham. The sper|matic animals of the calmar are three or four lines in length, and are visible without the assist|ance of the microscope. Their whole parts and organization are easily perceived. But they are by no means small calmars, as Leeuwen|hoek imagined. They are not even animated, though they have motion, but are only machines,

which ought to be regarded as the first union of the organic particles.

Though Leeuwenhoek had not this opportu|nity of undeceiving himself, he had, however, observed other appearances which ought to have had this effect. He had remarked, for example, that the spermatic animals of the dog* 1.49, often changed their figure, especially when the fluid was nearly evaporated; that, when dead, they had an opening in the head, which did not ap|pear when they were alive; and that the head was full and round, during the life of the pre|tended animal, and flat and sunk after its death; These circumstances should have led him to he|sitate concerning the real animation of these bodies, and to think that the phaenomena cor|responded more with a machine which emptied itself, like that of the calmar, than with the pro|perties of an animal.

I have said that the motion of these moving bodies, these organic particles, is not similar to the motion of animals, and that there is no in|tervals in their movements. Leeuwenhoek, in tom. 1. p. 168. makes precisely the same remark: 'Quotiescunque,' says he, 'animalcula in se|mine masculo animalium fuerim contemplatus, attamen illa se unquam ad quietem contulisse, me nunquam vidisse, mihi dicendum est, si mo|do sat fiuidae superesset materiae in qua sese commode movere poterant; at eadem in con|tinuo

manent motu, et tempore quo ipsis mori|endum appropinquante, motus magis magisque deficit, usquedum nullus prorsus motus in illis agnoscendus sit.' It is difficult to conceive, that animals should exist, which, from the mo|ment of their birth to their dissolution, should continue to move rapidly, without the smallest interval of repose; or to imagine that the sper|matic animals of the dog, which Leeuwenhoek perceived to be as active on the seventh day as the moment they proceeded from the body of the dog, should be able, during all this time, to move with a celerity which no animal on earth could persist in for a single hour, especially when the resistence arising from the density and tena|city of the fluid is taken into consideration. This species of continued motion, on the contrary, has an exact corresondence to the nature of the organic particles, which, like artificial machines, produce their effects by a continued operation, and stop immediately after the end is accom|plished.

In the numerous experiments made by Leeu|wenhoek, he doubtless observed spermatic animals without tails. He even mentions them in some places, and endeavours to explain the phaeno|menon. For example, speaking of the semen of the cod, he says* 1.50, 'Ubi vero ad lactium ac|cederem observationem, in iis partibus quas a|nimalcula esse censebam, neque vitam neque

caudam dignoscere potui; cujus rei rationem esse existimabam, quod quamdiu animalcula natando loca sua perfecte mutare non possunt, tam diu etiam cauda concinne circa corpus ma|neat ordinata, quodque ideo singula animalcula rotundum repraesentent corpusculum.' It would have been more simple, and more agreeable to truth, to have said, that the spermatic animals of this fish sometimes have tails, and sometimes have none, than to suppose that the tails were so exactly would round their bodies as to give them a spherical figure. One would be apt to think, that Leeuwenhoek had never fixed his eyes upon, or described any moving but those which had tails; he has given figures of none that wanted tails, because, though they moved, he did not regard them as animals. This is the reason why all Leeuwenhoek's figures of sper|matic animals are very similar, and all drawn with tails. When they appeared in any other form, he thought they were imperfect, or rather that they were dead. Besides, it is apparent from my experiments, that, instead of unfolding their tails, wherever they are placed in circumstances proper for swimming, as Leeuwenhoek insists, these pretended animals gradually lose their tails, in proportion to the rapidity of their motions, till, at last, these tails, which are bodies foreign to the animalcules, or threads which they drag after them, totally disappear.

Leeuwenhoek, speaking of the spermatic ani|mals of man* 1.51, says: 'Aliquando etiam ani|madverti inter animalcula particulas quasdam minores et subrotundas; cum vero se ea aliquo|ties eo modo oculis meis exhibuerint, ut mihi imaginarer eas exiguis instructas esse caudis, cogitare coepi annon hae forte particulae fo|rent animalcula recens nata; certum enim mihi est ea etiam animalcula per generationem pro|venire, vel ex mole minuscula ad adultam pro|cedere quantitatem: Et quis seit annon ea animalcula, ubi moriuntur, aliorum animalcu|lorum nutritioni atque augmini inserviant!' It appears from this passage, that Leeuwenhoek had seen, in the human semen, animalcules without tails; and that he is obliged to suppose them to be recently born, which is directly the reverse of what I have observed; for the moving bodies are never larger than when they separate from the filaments, which is the period that their mo|tion begins: But, as soon as they are fully disen|gaged from the mucilage, they become smaller, and continue to diminish till their motion entire|ly ceases. With regard to the generation of these animals, which Leeuwenhoek imagines to be cer|tain, no vestige of copulation has been discerned by the most acute observers. It is purely a ran|dom assertion, as may be easily proved from his own experiments. He remarks, for example,

with great propriety, that the milt of the cod* 1.52 is gradually filled with seminal liquor; and that, after the fish has spent this liquor, the milt dries, and leaves only a flaccid membrane, entirely destitute of every kind of fluid. 'Eo tempore,' says he, 'quo asellus major lactes suos emisit, rugae illae, seu tortiles lactium partes, usque adeo con|trahuntur, ut nihil praeter pelliculas seu membra|nas esse videantur.' How should this dry mem|brane, which contains neither seminal liquor nor animalcules, produce animalcules of the same spe|cies next season? If they were produced by a re|gular generation, such a long interruption could not take place, which, in most fishes, continues a whole year. To remove this difficulty, he af|terwards remarks: 'Necessario statuendum erit, ut asellus major semen suum emiserit, in lacti|bus etiamnum multum materiae seminalis gig|nendis animalculis aptae remansisse, ex qua ma|teria plura oportet provenire animalcula semi|nalia quam anno proxime elapso emissa fuerant.' This supposition, that part of the seminal liquor remains in the milt for the production of sper|matic animals the following year, is perfectly gratuitous, and contrary to observation; for the milt, during this interval, is nothing but a thin dry membrane. But how will he explain a phaenomenon that takes place in some fishes, and particularly in the calmar, whose seminal liquors are not only renewed every year, but even the

membranes which contain them. Here neither the milt nor the seminal liquor are preserved till the succeeding year; and, of course, their regular reproduction cannot be ascribed to generation. It is, therefore, apparent, that these pretended spermatic animals are not multiplied, like other animals, by generation; and this circumstance alone would entitle us to conclude, that the mo|ving particles in the seminal fluid are not real animals. Leeuwenhoek, though he tells us, in the passage above quoted, that the spermatic a|nimals are certainly propagated by generation, acknowledges, however, in another place* 1.53, that the manner in which these spermatic animals are produced, is exceedingly obscure, and that he leaves to others the farther elucidation of this subject. 'Persuadebam mihi,' says he, speaking of the spermatic animals of the dormouse, 'haecce animalcula ovibus prognasci, quia diversa in orbem jacentia et in semet convoluta videbam; sed unde, quaeso, primam illorum originem de|rivabimus! an animo nostro concipiemus ho|rum animalculorum semen jam procreatum esse in ipsa generatione, hocque semen tam diu in testiculis hominum haerere, usquedum ad annum aetatis decimum-quartum vel decimum-quintum aut sextum pervenerint, eademque animalcula tum demum vita donari, vel in justam staturam excrevisse, illoque temporis articulo generandi maturitatem adesse! sed haec

lampada aliis trado.' It is, perhaps, unneces|sary to make many remarks on what Leeuwen|hoek has here advanced. He saw, in the semen of the dormouse, spermatic animals which were round and without tails; in semet convoluta, says he, because he always supposes that they ought to have tails. He was formerly certain that these animals were propagated by genera|tion: Here he seems to be convinced of the re|verse. But, when he learned, that the vine|fretters (pucerons) were propagated without co|pulation * 1.54, he laid hold of this idea, in order to explain the generation of spermatic animals. 'Quemadmodum,' says he, 'animalcula haec quae pediculorum antea nomine designavimus (the pucerons) dum adhuc in utero materno latent, jam praedita sunt materia seminali ex qua ejusdem generis proditura sunt animalcula, pari ratione cogitare licet animalcula in semi|nibus masculinis ex animalium testiculis non migrare, seu ejici, quin post se relinquant mi|nuta animalcula, aut saltem materiam semina|lem ex qua iterum alia ejusdem generis ani|malcula proventura sunt, idque absque coitu, eadem ratione qua supradicta animalcula ge|nerari observavimus.' This supposition is not more satisfactory than the preceding; for, by thus comparing the generation of spermatic a|nimalcule with that of the vine-fretter, we dis|cover not the reason why they are never seen in

the human semen till the age of 14 or 15; nor do we learn whence they proceed, or how they are yearly renewed in fishes, &c. Notwith|standing all the efforts of Leeuwenhoek to esta|blish the generation of spermatic animals, he leaves the subject in the greatest obscurity, where it probably would have for ever remained, if we had not discovered, by the preceding expe|riments, that they are not animals, but organic moving particles, contained originally in the food, and found in vast numbers in the seminal liquors of animals, which are the most pure and most organic extracts derived from the food.

Leeuwenhoek acknowledges, that he did not always find animalcules in the male semen; for example, in that of the cock, which he often examined, he never but once saw the eel-like animalcules: And, some years after, he could not discover these eels* 1.55, but found animalcules with a large head and a tail, which his drawer could not perceive. He likewise remarks, that, during one season, he could not discover living animals in the seminal fluid of the cod* 1.56. All these disappointments proceeded from this cir|cumstance, that, though he saw moving glo|bules, he was unwilling to acknowledge them to be animals, unless they had tails, though it is in the form of globules that they most generally appear, either in seminal fluids, or in infusions

of animal and vegetables substances. In the same place, he remarks, that, though he had of|ten distinctly seen the spermatic animals of the cod, he was never able to make his drawer per|ceive them: 'Non solum,' says he, 'ob eximi|am eorum exilitatem, sed etiam quod eorum corpora adeo essent fragilia, ut corpuscula pas|sim dirumperentur; unde factum fuit ut non|nisi raro, nec sine attentissima observatione, ani|madverterem particulas planas atque ovorum in morem longas, in quibus ex parte caudas dignoscere licebat; particulas has oviformes ex|istimavi animalcula esse dirupta, quod particu|lae hae diruptae quadruplo fere viderentur majores corporibus animalculorum vivorum.' When an animal, whatever be its species, dies, it does not suddenly change its form; from being long like a thread, it does not become round like a bullet; neither does it become four times as large after death as before it. Not a single ar|ticle of what is advanced by Leeuwenhoek, in this passage, has the smallest correspondence to the nature of an animal; but, on the contrary, the whole agrees with a species of machines which, like those of the calmar, burst and empty themselves, after having performed their func|tions. To pursue this observation a little fur|ther: He tells us, that he has seen the spermatic animals of the cod under different forms, 'Mul|ta apparebant animalcula sphaeram pellucidam repraesentantia, and of different sizes,' 'Haec

animalcula minori videbantur mole, quam ubi eadem antehac in tubo vitreo rotundo exami|naveram.' This is an evident proof, that there is nothing like a uniform and invariable species in these animalcules, and, consequently, that they are not animals, but only organic moving par|ticles, which, by their different combinations, assume various figures and sizes. Of these or|ganic particles, vast numbers appear in the ex|tract and in the residue of our food. The mat|ter which adheres to the teeth, and which, in healthy persons, has the same smell with the se|minal fluid, is only a residue of our food. In it we accordingly find a great quantity of these pretended animals, some of which have tails, and resemble those of the seminal fluid. Mr Baker has given figures of four species of them, which are all a kind of cylinders, ovals, or glo|bules, some of them having tails, and others not. But, after the strictest examination, I am per|suaded, that none of them are real animals, and that they are only, like those in the semen, the organic living particles of the food appearing under different forms. Leeuwenhoek, who knew not how to account for these pretended animals in the matter adhering to the teeth, sup|poses them to proceed from certain species of food, as cheese, in which they previously exist|ed; but they are found among the teeth of e|very person, whatever kind of food be eaten; and, besides, they have no resemblance to mites,

or other animalcules which appear in corrupted cheese. In another place, he tells us that these teeth-animals proceed from the cistern-water which we drink, because he observed similar ani|mals in rain-water, especially when it had stag|nated upon leaden roofs. But, when we give the history of microscopic animals, we shall de|monstrate, that most of those found in rain-water are only organic moving particles, which divide, unite, change their size and figure, and, in a word, which can be made to move or to rest, to live or die, as often as we please.

Most seminal fluids spontaneously dilute, or be|come more liquid, when exposed to the air, or to a certain degree of cold, than when they issue from the body. But they thicken upon the ap|plication of a moderate degree of heat. I expo|sed some of these fluids to a degree of cold equal to that of water just beginning to freeze; but the pretended animalcules suffered not the least in|jury from it. They moved with equal activity, and during the same length of time, as those to which no cold had been applied. But those which were exposed to a small degree of heat, soon ceased to move, because the liquor thickened. If those moving bodies were animals, they dif|fered in their nature and constitution from all o|thers, to whom a moderate degree of heat com|municates force and motion, and upon whose bodies cold has the very opposite effects.

Before leaving this subject, upon which I have, perhaps, dwelt too long, I must still add another remark, which may lead to some use|ful conclusions. These pretended spermatic animals, which are nothing but the organic living particles of food, exist, not only in the seminal fluids of both sexes, and in the remnants of food that adhere to the teeth, but likewise in the chyle and in the excrements. Leeuwenhoek, having met with them in the ex|crements of frogs, and of other animals which he dissected, was at first greatly surprised; and, not being able to conjecture from whence ani|mals could proceed so similar to those in the se|minal liquor he had just been examining, he accuses his own want of dexterity, and supposes, that, in diffecting the animal, he had inadver|tantly opened the seminal vessels, and that the semen had in this manner been mixed with the faeces. But, having afterwards observed the same phaenomenon in the faeces of other ani|mals, and even in his own, he was then totally non-plussed. It is worthy of remark, that Leeuwenhoek never found animalcules in his own faeces, but when they were liquid. When|ever his stomach was out of order, and his belly was loose, the animalcules appeared; but, when his food was properly concocted, and his faeces were hard, not a single animalcule was to be found, although he diluted the faeces with wa|ter. These facts seem perfectly to coincide

with what we formerly advanced; for, when the stomach and intestines properly perform their functions, the faeces are only the gross dregs of the aliment, and all the nourishing and organic particles are absorbed by the lacteal ves|sels: In this case, we cannot expect to find or|ganic particles in the faeces, which are solely composed of the useless and inert part of our food. But, when the stomach and intestines, from any indisposition, allow the food to pass without being properly digested, then the orga|nic particles mix with the faeces; and, when examined with the microscope, we discover them in the form of living organic bodies. Hence we may conclude, that people who are troubled with looseness should have less seminal liquor, and be less fitted for the purposes of generation, than those of a contrary habit of body.

I have all along supposed that the female fur|nishes a fluid equally necessary to generation as that of the male. In the first chapter, I endea|voured to prove, that every organized body con|tains living organic particles; and, in Chap. II. and III. that nutrition and reproduction are ef|fects of the same cause; that nutrition is per|formed by absorption, or an intimate penetration of organic particles through all parts of the body; and that reproduction is effected by the superplus of these same organic particles, col|lected from every part of the body, and deposit|ed in reservoirs destined for that purpose. In

Chap. IV. I have shown how this theory applies to the generation of man, and other animals which have different sexes. Females being orga|nized bodies, as well as males, they must also have some reservoirs for the reception of the surplus of organic particles returned from all parts of their bodies. This surplus, as it is ex|tracted from every part of the body, must ap|pear in the form of a fluid; and it is this sluid to which I have given the appellation of the fe|male semen.

This fluid is not inert, as Aristotle pretends, but prolific, and equally essential to generation as the semen of the male. It contains particles distinctive of the female sex, as that of the other sex contains particles proper for the constitution of male organs; and each of them contain all the other organic particles which may be re|garded as common to both sexes: And hence, from a mixture of the two, the son may resem|ble his mother, and the daughter her father. Hippocrates maintains, that the semen consists of two fluids, one strong, which produces males, and the other weak, which produces females. But, as the seminal fluid is extracted from every part of the body, it is impossible to conceive how the body of a female should produce particles proper for the formation of male organs.

This liquor must enter, by some way or other, into the uterus of viviparous animals; and, in oviparous animals, it must be absorbed by the

eggs, which may be regarded as portable ma|trixes. Each of these matrixes, or eggs, con|tains a small drop of the female fluid, in that part which is called the cicatrice. This prolific drop, when the female has had no communica|tion with the male, assumes, as Malpighius ob|serves, the form of a mole or inorganic mass; but, when it is penetrated by the semen of the male, it produces a foetus, which is nourished and brought to perfection by the juices of the egg.

Eggs, therefore, instead of being common to all females, are only instruments employed by nature for supplying the place of uteri in those animals which are deprived of this organ. Instead of being active and essential to the first impreg|nation, eggs are only passive or accidental parts, destined for the nourishment of the foetus al|ready formed in a particular part of this matrix by the mixture of the male and female semen. Instead of existing from the creation, and each including within itself an infinity of males and females, eggs, on the contrary, are bodies com|posed of a superfluous part of the food, which is more gross, and less organic, than that of which the seminal fluid consists. The egg, in oviparous females, answers the same purposes as the uterus and menstrual flux in the vivipa|rous.

To evince that eggs are only destined by na|ture to supply the place of an uterus in such ani|mals

as are deprived of this organ, we have on|ly to consider, that females produce eggs inde|pendent of the male. The uterus, in viviparous animals, is a part peculiar to the female sex; in the same manner, female fowls, who want this organ, have the defect amply supplied by the successive production of eggs, which neces|sarily exist in these females, independent of all communication with the male. To pretend that the foetus pre-existed in the egg, and that eggs are contained, ad infinitum, within each other, is equally ridiculous as to maintain that the foetus pre-existed in the uterus, and that the uterus of the first female contained all the uteri that ever were or will be produced.

Anatomists have applied the term egg to things 〈◊〉〈◊〉 very opposite natures. Harvey, in his 〈◊〉〈◊〉, Omnia ex ovo, by the word egg, when applied to oviparous animals, means only the bag which includes the foetus and all its appendages. He imagined that he perceived the formation of this egg or bag immediately after the junction of the male and female. But this egg proceeded not from the ovarium of the female: He even asserts, that he could not di|stinguish the smallest alteration in the ovarium. It is apparent, that there is not here the most distant analogy to what is commonly understood by the word egg, unless, perhaps, the figure of the bag might have some faint resemblance to that of an egg. Harvey, though he dissected

many viviparous females, never could perceive any change in their ovaria: He even regards them as glands totally unconnected with the purposes of generation* 1.57, though, as we have seen, they undergo very considerable changes. This able anatomist was deceived by the small|ness of the glandular bodies in animals of the deer kind, to which his researches were princi|pally confined. Conradus Peyerus, who made many observations on the testicles of female deers, remarks, 'Exigui quidem sunt damarum testiculi, sed post coitum foecundum, in alter|utro eorum, papilla, sive tuberculum fibrosum, semper succrescit; scrofis autem praegnanti|bus tanta accidit testiculorum mutatio, ut me|diocrem quoque attentionem fugere nequeat* 1.58.' This author ascribes, with propriety, the reason why Harvey observed no changes in the testicles of the deer, to their smallness. But he is wrong when he tells us, that the changes he had re|marked, and which had escaped Harvey, never happened but after impregnation.

Harvey was deceived in several other essential articles. He insists, that the semen never enters into the uterus, and that it is impossible for it to find admittance; and yet Verheyen found a great quantity of male semen in the uterus of a cow, which he dissected six hours after copula|tion * 1.59. The celebrated Ruysch informs us, that,

in dissecting a woman who had been killed im|mediately after the act of adultery, he found a considerable quantity of male semen, not only in the uterus, but in the Fallopian tubes* 1.60. Valis|nieri likewise assures us, that Fallopius, and other anatomists, had discovered male semen in the u|teri of several women. This point, therefore, though denied by Harvey, is established by the positive testimony of several able anatomists, and particularly by Leeuwenhoek, who found male semen in the uteri of many different species of females.

Harvey mentions an abortion, in the second month, as large as a pigeon's egg, without any appearance of a foetus. In this also he must have been deceived; for Ruysch, and several o|ther anatomists, maintain, that the foetus is di|stinguishable by the naked eye, even in the first month of pregnancy. In the History of the French Academy, we have an account of a foe|tus compleatly formed on the twenty-first day after impregnation. If, to these authorities, we add that of Malpighius, who distinguished the chick in the cicatrice immediately after the egg issued from the body of the hen, we cannot hesitate in pronouncing that the foetus is form|ed immediately after copulation; and, conse|quently, no credit is due to what Harvey says concerning the increase of the parts by juxta-po|sition; since these parts exist from the beginning,

and gradually expand till the foetus be perfectly mature.

Graaf differs widely from Harvey in his ac|ceptation of the word egg. He maintains, that the female testicles are real ovaria, and contain eggs similar to those of oviparous animals, only that they are much smaller, never fall out of the body, nor detach themselves till after impregna|tion, when they descend from the ovarium into the uterus. The experiments of Graaf have contributed more to the belief of the existence of eggs, than those of any other anatomist. They are, notwithstanding, totally void of foundation; for this celebrated author, in the first place, mi|stakes the vesicles of the ovarium for eggs, though they are inseparable from the ovarium, form a part of its substance, and are filled with a species of lymph. 2. He is still more deceived, when he informs us, that the glandular bodies are on|ly the coverings of these eggs or vesicles; for it is certain, from the observations of Malpighius and of Valisnieri, and from my own experi|ments, that the glandular bodies contain no ve|sicles. 3. He is wrong in maintaining that the glandular bodies never appear till after impreg|nation. On the contrary, these bodies are uni|formly found in all females, after the age of puberty. 4. He errs in supposing that the glo|bules which he saw in the uterus, and which con|tained the foetuses, were the very vesicles that had descended from the ovarium into the uterus,

and that, he remarks, had become ten times smaller than when they were in the ovarium. This circumstance alone of their diminished size should have convinced him of his mistake. 5. He is not less unfortunate in maintaining that the glandular bodies are only the coverings of the fecundated eggs, and that the number of co|verings or empty follicles always correspond to the number of foetuses. This assertion is the reverse of truth; for, on the testicles of all fe|males, we uniformly find a greater number of glandular bodies, or cicatrices, than of foetuses actually produced; and they even appear in those which never brought forth. To this we may add, that neither he, Verheyen, nor any other person, ever saw the egg in this pretended co|vering, or in its follicle, though they have thought proper to rest their system upon that supposi|tion.

Malpighius, who distinguished the growth of the glandular bodies in the female testicle, was deceived when he imagined that he once or twice discovered the egg in their cavities; for this ca|vity contains only a fluid; besides, after number|less experiments, no man has ever been able to discover any thing that had the most distant re|semblance to an egg.

Valisnieri, who is never deceived with regard to facts, is wrong in maintaining that the egg must exist in the glandular body, though neither

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he, nor any man else, was ever able to discover it.

Let us now attend to what may be esteemed the real discoveries of these anatomists. Graaf was the first who discovered that the testicles of females suffered any change; and he was right in maintaining that they were parts essentially necessary to generation. Malpighius demonstra|ted, that the glandular bodies gradually grew to maturity, and that, immediately after, they were obliterated, and left behind them only a slight cicatrice. Valisnieri illustrated this subject still farther. He discovered that these glandular bodies were found in the testicles of all females; that they were considerably augmented in the season of love; that they increased at the ex|pence of the lymphatic vesicles of the testicle; and that, during the time of their maturity, they were hollow and full of liquor. These are all the truths we have learned concerning the pre|tended ovaria and eggs of viviparous animals: What conclusions are we to draw from them? Two things appear to be evident: The one, that no eggs exist in the testicles of females; the o|ther, that there is a fluid both in the vesicles of the testicle, and in the cavity of the glandular bodies; and we have demonstrated, in the pre|ceding experiments, that this last fluid is the true female semen, because it contains, like that of the male, spermatic animals, or rather organic par|ticles in motion.

The seminal fluid of females, therefore, be|ing thus fully ascertained, after what has been said, we must be satisfied that the seminal fluid in general is the superfluous organic part of our food, which is transmitted from all parts of the body to the testicles and seminal vessels of males, and to the testicles and glandular bodies of fe|males. This liquor, which issues through the nipples of the glandular bodies, perpetually be|dews the Fallopian tubes, and may casily find admission into them, either by absorption, or by the small aperture at their extremity, and in this manner may descend into the uterus. But, on the supposition of the existence of eggs, which are ten or twenty times larger than the aperture of the tubes, it is impossible to conceive the pos|sibility of their being transmitted to the uterus.

The liquor shed by females in the paroxysm of love, which Graaf supposes to proceed from lacunae about the neck of the uterus and the o|rifice of the urethra, may be a portion of the superfluous fluid that continually distills from the glandular bodies upon the Fallopian tubes. But perhaps this liquor may be a secretion of a dif|ferent kind, and no way connected with gene|ration. To decide this question, microscopic observations would be necessary; but all expe|riments are not permitted even to philosophers. I am inclined to think, that, in this liquor, the same spermatic animals, or moving bodies, would be found as appear in the fluid of the glandular

bodies. Upon this subject, I might quote the authority of an Italian physician, who had an opportunity of trying this experiment, which is thus related by Valisnieri* 1.61: 'Aggiugne il lo|dato sig. Bono d'avergli anco veduti (animali spermatici) in questa linfa o siero, diro cosi voluttuoso, che nel tempo dell' amorosa zuffa scappa dalle femine libidinose, senza che si po|tesse sospettare che fossero di que' del maschio,' &c. If the fact be genuine, as I have no rea|son to doubt, it is certain that this liquor is the same with that contained in the glandular bodies, and, of course, that it is a real seminal fluid, which escapes through the lacunae of Graaf, si|tuated about the neck of the uterus.

Hence we may conclude, that the most libidi|nous females will be the least fruitful, because they throw out of the body that fluid which ought to remain in the uterus for the formation of the foetus. We likewise learn why common prostitutes seldom conceive; and why women in warm climates, who have more ardent desires than those of colder regions, are less fertile. But of this we shall afterwards have occasion to treat.

It is natural to imagine that the seminal fluid of either sex should not be fertile, unless when it contains moving bodies. But this point is still undetermined. The Italian physician, mentioned above, alledges, that he never found spermatic

[figure]

Plate X.

animals in his semen till he arrived at 40 years, although he was the father of many children, and continued, after the animalcules appeared, to beget more.

The spermatic moving bodies may be regarded as the first assemblages of the organic particles which proceed from all parts of the body; and, when a great number of them unite, they become perceptible by means of the microscope. But, when the number united is small, the body they form is too minute to be visible, and no motion will appear in the seminal fluid, a case which not unfrequently happens. But a long train of suc|cessive experiments would be necessary to ascer|tain the causes of the different states in which this fluid appears.

Of one thing I am certain, from repeated tri|als, that a seminal liquor, though no motion can be perceived when it is first taken from the bo|dy, after being three or four days infused in water, produces as great a number of organic moving particles, as another semen, treated in the same manner, which at first contained vast multitudes. These moving bodies appear like|wise in infusions of the blood, of the chyle, of the flesh, and even of the urine, as well as in infusions of all parts of vegetables; and those which appear in all these different substances, seem to have nothing peculiar to them. They all move and act nearly in the same manner. If we will have these bodies to be animated, it must be al|lowed,

that they are very imperfect, and ought to be regarded only as the rudiments of animals, or rather as bodies composed of particles essen|tial to the existence of animals. As Nature's productions are uniform, and advance by imper|ceptible degrees, there is no improbability in supposing the existence of organized bodies which properly belong not either to the animal or ve|getable kingdoms.

However this matter may stand, it is fully a|scertained, that all animal and vegetable sub|stances contain an infinite number of living or|ganic particles. These particles successively as|sume different forms, and different degrees of activity, according to different circumstances. They are more abundant in the seminal fluids of both sexes, and in the seeds of plants, than in a|ny other part of the animal or vegetable. There exists, therefore, in vegetables and animals, a li|ving substance which is common to them both; and this substance is the matter necessary to their nutrition. The animal is nourished by vegeta|ble or animal substances; and the vegetable is nourished by the same substances in a decompo|sed state. This common nutritive substance is always alive and active. It produces an animal or a vegetable, whenever it finds an internal mould or matrix accommodated to the one or the other, as has already been explained. But, when this active substance is collected too abun|dantly in a place where it has an opportunity of

uniting, it forms, in the animal body, other li|ving creatures, as the tape-worm, the ascarides, the worms sometimes found in the veins, in the sinuses of the brain, in the liver, &c. Animals of this kind owe not their existence to the ge|neration of individuals of the same species. It is, therefore, natural to think, that they are produced by an extravasation of the organic matter, or by an inability in the lacteal vessels to absorb the quantity of it presented to them. But we shall afterwards have occasion to exa|mine more in detail the nature of these worms, and of other animals which are produced in a similar manner.

When this organic matter, which may be con|sidered as an universal semen, is assembled in great quantities, as in the seminal fluids, and in the mucilaginous part of the infusions of plants, its first effect is to vegetate, or rather to produce vegetating beings. These zoophytes swell, ex|tend, ramify, and then produce globular, oval, and other small bodies of different figures, all of which enjoy a species of animal life; they have a progressive motion, which is sometimes very rapid, and sometimes more slow. The globules themselves decompose, change their figure, and become smaller; and, in proportion as they di|minish in size, the rapidity of their motion in|creases.

I have sometimes imagined, that the venom of the viper, and even the poison of enraged ani|mals,

might proceed from this active matter be|ing too much exalted. But I have not yet had leisure for experiments of this kind, nor for a|scertaining the nature of different drugs. All I can say at present is, that infusions of the most active drugs abound with moving bodies, and that they appear sooner in them than in other substances.

Almost all microscopic animals are of the same nature with the moving bodies in the seminal fluids, and in infusions of animal and vegetable substances. The eels in paste, in vinegar, &c. are all of the same nature, and derived from the same origin. But the proofs and illustrations relative to this subject, we shall reserve till we give the particular history of microscopic a|nimals.

CHAP. IX.

Varieties in the Generation of Animals.

THE nutrition and the reproduction of a|nimals and of vegetables, are thus effected by the same matter. It is a substance universal|ly prolific, and composed of organic particles, the union of which gives rise to all organized bodies. Nature always works on the same stock, and this stock is inexhaustible. But the means she employs to give it value are various; and these general varieties and affinities merit the at|tention of philosophers, because from them we are enabled to account for particular exceptions to the common plan of her operations.

In general, large animals are less prolific than small ones. The whale, the elephant, the rhi|noceros, the horse, man, &c. produce but one, and very rarely two, at a birth. But small ani|mals, as rats, herrings, and insects, produce a great number. Does this difference proceed from the greater quantity of nourishment ne|cessary to support the large animals than the small, and from the former having a less pro|portional quantity of superfluous nutritive par|ticles,

capable of being converted into semen, than the former? It is certain, that the small animals eat more, in proportion to their bulk, than the large. But it is likewise probable, that the prodigious increase of the smaller animals, as bees, flies, and other insects, may be owing to the extreme fineness and delicacy of their or|gans and members, by which they are enabled to select the most substantial and most organic parts of the animals and vegetables, from which they extract their nourishment. A bee, which lives upon the purest and most refined parts of flowers, receives from its food a greater propor|tional quantity of organic particles than a horse, who feeds upon hay, straw, and the grosser parts of vegetables. The horse, accordingly, produ|ces but one at a time, while the bee produces many thousands. The oviparous animals are, in general, smaller than the viviparous, and they are likewise much more prolific. The long time that the foetus remains in the uterus of vivipa|rous animals, is another obstacle to multiplica|tion: During gestation, and the suckling of the young, no new generation can take place. But the oviparous animals, which produce, at the same time, both uterus and foetus, and throw them out of the body, are almost perpetually in a condition to reproduce; and it is well known, that, if a hen be prevented from sitting, and be fully fed, the number of her eggs may be great|ly increased. If hens lay not while they brood,

it is because they cease to eat; and for this pur|pose they leave not their nests but once a day, and even then for a very short time, lest their eggs should be injured by the cold. During this operation, they take not above one tenth part of their ordinary nourishment.

Animals which produce but one at a birth, ac|quire nearly their full growth before they are fit for generating. But those which produce many, generate before they are half grown. Man, the horse, the ass, the sheep, are incapable of gene|ration till after they have nearly acquired the greatest part of their growth. It is the same with pigeons and other birds that lay but a small number of eggs: But those that are more pro|lific, as cocks and hens, fishes, &c. begin to ge|nerate much sooner. A cock is capable of this operation at the age of three months, when he is not above one third of his full size. A fish, which, in 20 years, will weigh 30 pounds, ge|nerates the first or second year, when it weighs not, perhaps, more than half a pound. But ex|periments are still wanting to ascertain the growth and duration of fishes: Their age may be dis|covered by examining with a microscope the an|nual rings or strata of which their scales are composed. But we are ignorant how far this may extend. I have seen, in the Count de Maurepas' ponds, carps which were well attested to be at least 150 years old, and they appeared to be equally active and lively as common carps.

I will not say with Leeuwenhoek, that fishes are immortal, or, at least, that they cannot die of old age. Every thing, in time, must perish. Whatever has an origin, a birth, or commence|ment, must arrive at a termination or death. But fishes, by living in a uniform element, and being sheltered from the injurious vicissitudes of the air, must continue longer in the same state than other animals, especially if these vicissitudes, as Bacon remarks, be the chief causes of the destruction of animated beings. But the prin|cipal cause of the longevity of fishes is, that their bones are softer than those of other animals, and do not perceptibly harden with age. The bones of fishes lengthen, and turn thick without ac|quiring more solidity. But the density of the bones of other animals continually increases; and, when their interstices are completely filled and obstructed, the circulation of their fluids ceases, and death ensues. But, in the bones of fishes, this augmentation of solidity, which is the natural cause of death, proceeds in such an im|perceptible manner, that they must live very long before they can feel any of the effects of old age.

All quadrupeds covered with hair are vivipa|rous, and those covered with scales are ovipa|rous. The close texture of the shells or scales of oviparous animals prevents them from losing so much matter by transpiration, as makes its way through the porous skins of the viviparous.

May not this retention of superfluous nourish|ment, which cannot escape by transpiration, be one reason of the extraordinary fertility of these animals, and of their being able to subsist a long time without food? All birds and flying insects are oviparous, except some species of flies which produce their young alive* 1.62. These have no wings immediately after their birth; but they gradually shoot out as the animal advances in growth; and they are not in a condition to be used till it acquires full maturity. All shell|fishes are viviparous; and likewise those reptiles that have no feet, as snakes and serpents; they change their skins, which are composed of small scales. The viper is but a slight objection to this general rule; for it is not properly vivipa|rous. It first produces eggs, from which the young are hatched: This operation is indeed carried on and compleated in the body of the mother; and, in place of laying the eggs, like other oviparous animals, the viper hatches them within the body. The salamander, in which, as Maupertuis remarks* 1.63, both eggs and young are found at the same time, is a similar exception in oviparous quadrupeds.

Most animals are multiplied and perpetuated by copulation. But many animals, as the great|est number of birds, propagate rather by a kind of compression, than a proper copulation. Some

birds, indeed, as the ostrich, the male duck, &c. have considerable members, and propagate by a real intromission. Male fishes approach the fe|males in the season of spawning. They seem to rub their bellies against each other; for the male often turns on his back to meet the belly of the female. But no actual copulation takes place. The part necessary for this operation does not exist; and the males only approach the females for the purpose of shedding the liquor of their milts upon the eggs, which at that sea|son drop from the females. The male seems to be more attached to the eggs than to the female; for, when she ceases to throw out the eggs, the male instantly abandons her, and follows, with ardor, the eggs which are carried down by the stream, or dispersed by the winds. He passes and repasses a thousand times over every place where he finds eggs. It is not, surely, for the love of the mother that he makes all these move|ments: He cannot even be supposed to know her; for he has been often seen shedding his semen promiscuously on all the eggs that came in his way, without having ever met with the female to which they belonged.

Thus some animals are distinguished by sexes, and endowed with members proper for copula|tion. There are others which likewise have sexes, but want the necessary members. Others, as snails, have both members and sexes in each individual. Others, as the vine-fretters, have

no sexes, are equally fathers or mothers, and pro|duce of themselves without copulation. Though they seem to copulate at pleasure, we are unable to discover the use of their junction, or whether it be really a sexual embrace; unless we should suppose Nature to have endowed this small in|sect with generative faculties superior to those of any other species of animals, and to have be|stowed on every individual not only the power of reproduction, but likewise the power of mul|tiplying by sexual communications.

But, whatever varieties take place in the ge|neration of different species of animals, Nature prepares the body for it by a new production, which, whether it be external or internal, always precedes generation: Immediately before the season of impregnation, the ovaria of oviparous animals, and the testicles of the females of the viviparous, undergo a considerable change. The oviparous animals produce eggs, which gradual|ly increase in size, till they quit the ovarium and fall into the canal of the uterus, where they receive their white, their membranes, and their shell. This production marks the fecundity of the female, and without which generation could not be effected. In viviparous females, in the same manner, one or more glandular bodies ap|pear upon the testicles, which gradually grow under the membranes that covers them. These glandular bodies increase, and pierce, or rather elevate the membrane of the testicle; and, when

they arrive at maturity, a fissure, or several little holes, appear at their extremities, through which the seminal fluid escapes, and falls into the ute|rus. These glandular bodies are new produc|tions, which always precede generation, and without which it could not be effected.

Males undergo a similar change before they are fit for the purposes of generating. In the oviparous animals, the seminal reservoirs are filled, and sometimes the reservoirs themselves are annually renewed. The milts of some fishes, and particularly of the calmar, are renewed every year. The testicles of birds, immediately be|fore the season of their amours, swell to an e|normous degree. The testicles of the males of viviparous animals, especially of those which have seasons, likewise swell considerably; and, in ge|neral, the genitals of every species suffer an e|rection, which, though it be external and casu|al, may be regarded as a new production that necessarily precedes the faculty of generating.

Thus, in all animals, whether male or female, generation is always preceded by new produc|tions; and, when there is properly no new pro|ductions, some of the parts swell and extend to a remarkable degree. In some animals, not on|ly a new production appears, but their whole bodies are renewed, before generation can be effected; as happens in the surprising metamor|phosis of insects, which seems to be intended for no other purpose than to enable these ani|mals

to propagate their species; for their bodies are full grown before they are transformed. The insect, immediately before its transforma|tion, ceases to take nourishment; and it has no organs proper for generation, no means of con|verting the nutritive particles, with which it a|bounds more than any other species of animals, into eggs, or a seminal fluid. Hence the whole of this great surplus of nutritive particles at first unites and moulds itself into a form nearly re|sembling that of the original animal. The ca|terpillar becomes a butterfly, because, having no organs of generation, no reservoirs for contain|ing the superfluous nutritive particles, and, con|sequently, being incapable of producing minute organic bodies similar to the animal itself, the organic nutritive particles, which are always ac|tive, assume, by their union, the form of a but|terfly, partly resembling that of a caterpillar, both internally and externally, excepting that the parts of generation are unfolded, and ren|dered capable of receiving and transmitting the nutritive organic particles which form the eggs, and individuals peculiar to the species. The individuals produced by the butterfly ought not to be butterflies, but caterpillars; because it was the caterpillar that received the nourishment, and because the organic particles of this nourish|ment must therefore be assimilated into the form of a caterpillar, and not of a butterfly, which is only an occasional production of the superfluous

nourishment that precedes the real production of animals of this species, and a method employed by Nature to accomplish the important purposes of generation, similar to the production of glan|dular bodies, and of milts, in other animals.

When the superabundant quantity of organic nutritive particles is not great, as in man, and most large animals, generation does not take place till the growth of the body is nearly com|pleted; and even their prolific powers are limit|ed to a small number of young: But, when these particles are more abundant, as in birds, and o|viparous fishes, generation is effected before the animal be fully grown, and the production of individuals is very numerous. When the quan|tity of organic nutritive particles is still greater, as in insects, it first produces a large organized body, retaining the internal and essential consti|tution of the animal, but differing in several parts, as the butterfly differs from the caterpil|lar; and then it quickly generates an amazing number of young, similar to the animal that first prepared the organic nourishment from which they derived their origin. Lastly, when the quantity of superfluous nourishment is very great, and when the animal, at the same time, possesses the organs necessary to generation, as in the vine-fretters, it first confers on each indi|vidual the power of generating, and then a transformation, like that which other insects undergo: The vine-fretter becomes a flie; but

it can produce nothing, because it is only the residue of the organic particles that had not been employed in the production of the young.

Almost all animals, man excepted, have cer|tain annual seasons appropriated to the purposes of generation. To birds, spring is the season of love: Carps, and several other fishes, spawn in June and August. Pikes, and some other fishes, spawn in the spring. Cats have three seasons annually, in the months of January, May, and September. The roe-deer rut in December, wolfs and foxes in January, horses in summer, stags in September and October; and almost all insects generate only during the autumn. Some animals, as the insects, are totally exhausted by generation, and die soon after it. Others, though they die not, become feeble, are much ema|ciated, and require a considerable time to re|pair the great waste of their organic substance. Others are less affected, and are capable of frequently renewing their amours; lastly, man is very little affected, or, rather, he quick|ly repairs the loss, and therefore is, at all times, in a condition for propagating. All these varieties solely depend on the particular con|struction of the animal organs. The limits fix|ed by Nature upon the modes of existing are e|qually conspicuous in the manner of taking and digesting the food, in the means employed for retaining or throwing it out of the body, and in the instruments by which the organic particles

necessary to reproduction are extracted. And, upon the whole, it is apparent, that every thing exists which can exist.

The times of the gestation of females are e|qually various: Some, as mares, carry their young from eleven to twelve months; others, as women, cows, and hinds, carry their young nine months; others, as foxes and wolves, carry five months; bitches carry nine weeks, cats six weeks, and rabbits thirty-one days. Most birds are hatched in twenty-one days; though some of them, as the thistle-finches, hatch in thirteen or fourteen days. Here the variety is equally great as in every other part of the oeconomy of ani|mals: The largest animals produce fewer young, and carry them longest; which confirms the doc|trine, that the quantity of organic nourishment is proportionally less in large than in small ani|mals; for the foetus derives its growth and the expansion of its parts from the superfluous nou|rishment of the mother; and, as this growth requires longer time in large than in small animals, it is a proof that the quantity of or|ganic particles is not so great in the former as in the latter.

Animals, therefore, are much diversisied as to the time and manner of gestation, of engender|ing, and of producing; and this variety origi|nates from the very causes of generation. For, though the organic matter, which is common to every thing that lives or vegetates, be the gene|ral

principle of reproduction, the manner of its union, and the combinations it forms, must be infinitely varied, that the whole may become the sources of new productions. My experiments clearly demonstrate, that there are no pre-exist|ing germs, and that the generation of animals and vegetables is not univocal. There are, per|haps, as many beings, which either live or vege|tate, produced by a fortuitous assemblage of or|ganic particles, as by a constant and successive generation. It is to such productions that we ought to apply the axiom of the antients, Cor|ruptio unius, generatio alterius. The corruption and resolution of animals and vegetables pro|duce an infinite variety of organized bodies: Some of them, as those of the calmar, are only a kind of machines, which, though exceedingly simple, are very active. Others, as the sper|matic animalcules, seem to imitate the move|ments of animals. Others resemble vegetables in their manner of growth and expansion. There are others, as those of blighted wheat, which, at pleasure, can be made alternately to live or to die; and it is difficult to know to what they should be compared. There are still others, and in great numbers, which are at first a kind of animals, then become a species of vegetables, and again return alternately to their vegetable state. The more we examine this species of organized bo|dies, we shall probably discover greater and more singular varieties of them, in proportion as they

are farther removed from our observation, and from the structure of other animals with which we are already acquainted.

For example, blighted corn, which is effected by an alteration or resolution of the organic substance of the grain, is composed of multitudes of small organized bodies resembling eels. When infused in water for ten or twelve hours, we discover them to have a distinct wreathing, and a small degree of progressive motion. They cease to move as soon as the water fails them; and their motion commences upon the addition of fresh water: This alternate death and revivis|cence may be repeated for months, and even for years; so that these small machines may be made to act as long and as often as we please, without destroying or diminishing their force. They are a species of machines, which begin to act whenever they are immersed in a fluid. These fi|laments sometimes open like the filaments of the semen, and produce moving globules: We may, therefore, conclude them to be of the same nature, excepting that they are more fixed and solid.

The eels in paste have no other origin than the union of the organic particles of the most essential parts of the grain. The first eels which appear are certainly not produced by other eels; but, though they are not propagated themselves, they fail not to engender other living eels. By cutting them with the point of a lancet, we dis|cover

smaller eels issuing in great numbers out of their bodies. The body of this animal seems to be only a sheath or sac containing a multitude of smaller animals, which perhaps are other sheaths of the same kind, in which the organic matter is assimilated into the form of eels.

A great number of experiments would still be necessary to distinguish these animals, which are so singular and so little understood, into classes and genera. Some of them may be regarded as real zoophytes, which enjoy a kind of vege|tation, and which, at the same time, seem to wreath and move like animals. Others appear, at first, to be animals, and then join and form a species of vegetables. A small attention to the resolu|tion of a single grain of corn will elucidate, at least in part, what I have said on this subject. I might add other examples; but those I have gi|ven were only produced for the purpose of exhi|biting the varieties of generation. There are unquestionably several organized bodies which we consider as real animals, but which are not engen|dered by others of the same species. Some of them are only a kind of machines; and some of these machines have a certain limited effect, and act only for a certain time, as the machines in the milt of the calmar; others may be made to act as long and as often as we please, as those of blighted grain. There are vegetables which produce animated bodies, as the filaments of the human semen, from which active globules issue

and move by their own powers. In the corrup|tion, the fermentation, or rather in the resolu|tion of animal or vegetable substances, we find real animals capable of propagating their species, though they were not themselves produced in this manner. These varieties are, perhaps, more extensive than we imagine. Though it be right to generalize our ideas, to assemble the effects of Nature under one point of view, and to class her productions; yet numberless shades, and even degrees, in the great scale of being, will always escape our observation.

CHAP. X.

Of the Formation of the Foetus.

FROM the experiments of Verheyen, who found the semen of the bull in the uterus of a cow, and from those of Ruysch, Fallopius, and Leeuwenhoek, who discovered male semen in the uteri of women and many other animals, it seems to be a point fully ascertained, that the semen of the male enters into the uterus of the female. It is probable, that, during the time of coition, the orifice of the uterus opens for the reception of the seminal fluid: But, though this should not happen, the active and prolific part of the semen may penetrate the membranes and substance of the uterus itself; for, as the semi|nal liquor, as formerly remarked, is almost en|tirely composed of organic particles, which are very active, and extremely minute, they may pass with the utmost facility through the mem|branes and substance of the uterus.

What proves that the active part of this fluid may pass through the pores and substance of the uterus, is the sudden change it undergoes immediately after conception. The menses are

obstructed, the uterus becomes flaccid, swells, and appears to be inflated. All these changes must be effected by an active external cause, by the penetration of part of the seminal fluid into the substance of the uterus. This penetration is not confined to the surface; it extends through all the vessels and parts of which the uterus is composed, like that penetration by which nu|trition, and the expansion of the body is pro|duced.

We shall the more easily believe this to be the case, when we reflect, that, during the time of gestation, the uterus not only augments in size, but even in its quantity of matter, and that it possesses a species of life, or rather of vegetation, which continues till the child be delivered. If the uterus were only a sac, a reservoir for re|ceiving the semen and retaining the foetus, it would extend and diminish in thickness, in pro|portion as the foetus grew larger. But the aug|mentation of the uterus is not a simple exten|sion or dilatation of its parts. It not only extends as the foetus enlarges, but it acquires, at the same time, an additional thickness and solidity; or, in other words, both its size and quantity of matter are greatly increased. This augmenta|tion is a real growth or increase of substance, similar to the expansion of the body in young animals, which could not be effected but by an intimate penetration of organic particles analo|gous to the substance of those parts. As this

expansion of the uterus never happens but after impregnation, the seminal liquor must be the cause by which it is produced; for the uterus is considerably augmented before the foetus has acquired bulk enough to dilate it by pressing a|gainst its internal surface.

It appears, from my own experiments, to be equally certain, that the female has a seminal fluid, which begins to be formed in the testicles, and is brought to maturity in the glandular bo|dies. This fluid perpetually distills through the small apertures in the extremities of these bo|dies, and, like that of the male, enters the uterus by two different ways, either through the aper|tures at the extremities of the horns of the ute|rus, or by piercing through the substance of the uterus itself.

These two seminal fluids are extracts from all parts of the body; and a mixture of them is all that is necessary for the formation of a certain number of males and females. The more any animal abounds in this seminal fluid, or the more it abounds in organic particles, the number of young is the greater, as may be remarked in the smaller animals; and the number of young di|minishes in proportion as the organic particles are less abundant, as is the case with the larger animals.

But, before taking any farther notice of other animals, we shall examine with attention the formation of the human foetus. In mankind, as well as in the larger species of animals, the

quantity of organic particles in the male and fe|male semen is not great, and, accordingly, they very seldom produce above one foetus at a time. This foetus is either a male or a female, accor|ding as the number of organic particles predo|minates in the male or in the female fluid; and the child resembles the father or the mother most, according to the proportional quantities of male or female organic particles in the mixture of the two liquors.

I conceive, therefore, that the seminal fluids, both of the male and of the female, are equally active, and equally necessary for the purposes of propagation: And this, I think, is fully proven by my experiments; for I found in both fluids the same moving bodies; I discovered that the male fluid enters into the uterus, where it meets with the fluid of the female; that these two fluids are perfectly analogous; and that they are composed of parts not only similar in their form, but in their action and movements* 1.64. Now, I imagine, that, by the mixture of the two fluids, the activity of the organic particles proper to each is stopped; that the action of the one coun|t••••••alances the action of the other; that each or|g••••ic particle, by ceasing to move, remains fixed in the place which corresponds to its nature; and that this place can be no other than that which it formerly occupied in the body of the animal from which it was extracted. Thus all the orga|nic particles which were detached from the head

of the animal, will arrange themselves in a si|milar order in the head of the foetus. Those which proceeded from the back bone, will dispose themselves in an order corresponding to the structure and position of the vertebrae. In the same manner, the organic particles which had been detached from any part of the body, will naturally assume the same position, and arrange themselves in the same order that they observed before they were separated from that part. Of course, these particles will necessarily form a small organized body, entirely similar to the ani|mal from which they originally proceeded.

It is worthy of remark, that this mixture of the organic particles of both sexes contains par|ticles that are similar, and particles that are dis|similar. The similar particles are those which have been detached from all the parts that are common to the two sexes. The dissimilar particles are those which have been separated from the parts that distinguish the two sexes. In this mixture, therefore, there is a double portion of particles de|stined for the formation of the head, the heart, and such parts as are common to both sexes; while there are no more than what are necessary for the production of the sexual parts. Now, the similar particles may act upon each other without pro|ducing any disorder; and they may unite in the same manner as if they had proceeded from the same body. But the dissimilar parts cannot act upon each other, nor form any intimate union, because they have no analogy or relation: Hence

these particles will preserve their original nature without any mixture, will first fix their position, without the necessity of being penetrated by o|thers. Thus the particles which proceed from the sexual parts will be first fixed, and those that are common to the two sexes, whether they be|long to the male or to the female, will then six indiscriminately, and form an organized body, which, in its sexual parts, will perfectly resemble the father, if it be a male, and the mother, if it be a female, but, which, in the other parts, may resemble either or both.

If what I have advanced be properly under|stood, we shall, perhaps, be able to obviate an objection made to the system of Aristotle, and which might also be urged against the doctrine which I am now establishing. The question is, Why is not every individual, both male and fe|male, endowed with the faculty of producing an animal of its own sex? I am aware of the diffi|culty of solving this question, which I have slightly mentioned in the fifth chapter, and shall now proceed farther to illustrate.

From what is delivered in the first four chap|ters, and from the experiments I have described, it is apparent, that reproduction is effected by the assemblage and union of the organic par|ticles, detached from every part of the animal or vegetable body, in one or several common re|servoirs; that these particles are the same which serve for the nutrition and expansion of the

body; and that both effects are produced by the same matter, and by the same laws. I think I have established this point by so many facts and rea|sonings, that it is impossible to entertain a doubt concerning its truth. But, I allow, that the question may be put, Why every separate animal and vegetable produces not its own likeness, since every individual detaches from all its parts, and collects in a common reservoir, the organic particles necessary for the formation of a small organized body? Why is not this organized body formed? and why, in most animals, is a mixture of the fluids of both sexes necessary? If I were to reply, that in all the vegetable tribes, in all those animals that multiply by cutting, and in the vine-fretters, which produce without any sexual commerce, the general intention of Nature seems to be, that each individual should multiply its own species, and that reproduction by the intervention of sexes is only an exception to this general law. It might, with propriety, be rejoined, that the exception is perhaps more universal than the rule itself. To maintain that all individuals would have the faculty of re|producing, if they were endowed with proper organs, and if they contained the matter neces|sary for nourishing the embryo, is not removing the difficulty: For, in females, all these circum|stances concur; and yet the influence of the male is indispensible to the production either of a female or of a male foetus.

But, we come nearer a solution of the ques|tion, when we maintain, that, though the fluid in the testicles and seminal vessels of the male contain all the organic particles necessary for the formation of a male foetus, yet these particles cannot receive any local establishment or ar|rangement of parts, because a constant circula|tion of them goes on by means of absorption, and by the perpetual succession of new supplies from all parts of the body; and that, as the same circulation of the organic particles takes place in the female, neither of them can pos|sibly multiply without the assistance of the other; because, in the mixture of the male and female fluids, the different organic particles of which they consist have a greater affinity to each other than they have to the body of the female where the mixture happens. But, though this explication were admitted, why, it may still be asked, does not the ordinary mode of gene|ration correspond with it? For, upon this sup|position, each individual would produce, and, like snails, mutually impregnate one another, every individual receiving the organic particles furnished by the other, which, without being injured by any other power, would unite solely by the affinity between the particles themselves. If there were no other cause by which the or|ganic particles could be united, perhaps this mode of generation would be the most simple. But it is contrary to the analogy of Nature.

Few animals are endowed, like snails, with both sexes; and, therefore, if this mode of propa|gating were the most simple, it would be more generally employed by Nature. This solution, of course, amounts to no more than a gratuitous supposition, that males produce not, solely be|cause they have not organs proper for contain|ing and nourishing a foetus.

It may be still farther supposed, that the acti|vity of the organic particles in the semen of each individual requires to be counterbalanced by the force or action of those of the other individual, in order to reduce them to a fixed state, or e|quilibrium, without which the formation of the foetus cannot be effected; and that the motion of the organic particles of the female cannot be counterbalanced by any other cause than a con|trary action in the organic particles received from the male. But this answer is too general to be void of obscurity. However, when we attend to all the phaenomena, it may, perhaps, admit of some illustration. The mixture of the two seminal fluids produces not only a male or fe|male foetus, but other organized bodies, which are endowed with the faculty of growth or ex|pansion. The placenta, the membranes, &c. are produced at the same time, if not sooner, than the foetus. There are, therefore, in the seminal fluid of the male or female, or in the mixture of both, organic particles not only suit|ed to the production of the foetus, but of the

placenta and membranes. Since there are no parts either in the male or female bodies from which they could be detached, whence do these particles proceed? It must be admitted, that the organic seminal particles of each sex being equally active, uniformly produce organized bodies every time that they can six themselves, by their mutual action upon one another; that, of the particles destined to produce a male, those peculiar to the male sex will fix first, and form the sexual parts; that the particles common to both sexes may afterwards fix themselves indif|ferently, in order to form the rest of the body; and that the placenta and membranes are pro|duced by the excess of organic particles which have not been employed in the formation of the foetus. If, as we have supposed, the foetus be a male, all the organic particles peculiar to the female sex, which have not been employed, as also the superfluous particles of both individuals which have not entered into the composition of the foetus, and which cannot be less than one half of the whole, remain for the formation of the membranes and placenta. If the foetus be a female, the same quantity of superfluous organic particles still remain, and are occupied in forming the placenta and membranes.

But it may be said, that the membranes and placenta, upon this supposition, ought to become another foetus, which would be a male, if the first was a female, and a female, if the first was

a male; because the first foetus consumed only the organic particles peculiar to the sex of one individual, and the half of those particles which were common to both sexes; and, of course, the sexual particles of the other individual, and the other half of the common particles, remain still unexhausted. To this I reply, that the first union of the organic particles prevents a second, at least under the same form; and that the foe|tus, being first formed, exerts an external force which destroys the natural arrangement of the other organic particles, and throws them into that order which is necessary for the formation of the placenta and membranes.

From the experiments and observations for|merly made, it is apparent, that all animated be|ings contain an amazing quantity of living or|ganic particles. The life of an animal or vege|table seems to be nothing else than a result of all the particular lives (if the expression be ad|missible) of each of these active particles, whose life is primitive, and perhaps indistructible. These living particles we have found in every animal and vegetable substance; and we are certain, that all these particles are equally ne|cessary to the nutrition, and, consequently, to the reproduction of animals and vegetables. That the union of a certain number of these particles, therefore, should produce an animated being, it is not difficult to conceive. As each particle is animated, a whole, or any assemblage of them,

must be endowed with life. These living or|ganic particles being common to all animated beings, they are capable of forming particular species of animals, or of vegetables, according to the peculiar arrangement they assume. Now, this arrangement depends entirely on the form of the individuals which furnish the organic particles. If they are furnished by an animal, they arrange themselves under the form pecu|liar to its species, exactly agreeable to that ar|rangement they observed when they nourished or expanded the animal itself. But, does not 〈…〉〈…〉 suppose the necessity of some base or centre, round which the particles assemble in order to unite and form a foetus? This basis is furnished by the particles which form the sexual parts. I shall illustrate this point.

As long as the organic particles of either sex remain alone, their activity produces no effect, because it is not opposed by any resistance or re|action from particles of a different kind. But, when the male and female liquors are blended, the particles detached from the sexual parts be|ing of a different kind, serve as a base to fix the activity of the other particles.

Upon this supposition, that the organic par|ticles which, in the mixture of the two fluids, represent the sexual parts of the male, can alone serve as a basis to the particles which proceed from all parts of the female; and that those proceed|ing from all parts of the male can only be fixed

by the particles which are detached from the sexual parts of the female; we may con|clude, that the sexual parts of the male foe|tus are formed by the organic particles of the father, and the rest of its body by the organic particles of the female; and, on the contrary, that the female foetus derives nothing but its sex from the mother, and the rest of its body from the father. Boys, therefore, excepting in the parts which distinguish their sex, ought to resemble the mother more than the father, and girls should resemble the father more than the mother.

Considering generation by sexes under this light, we should conclude it to be the most com|mon manner of reproduction, as it is in reality. Beings of the most perfect organization, as ani|mals, whose bodies make a whole that is inca|pable of division, and whose powers are all con|centrated into one point, cannot be reproduced in any other way; because they contain only particles that are perfectly similar, and cannot be united but by means of different particles furnished by another individual. But vegetables, which are less perfect in their organization, and which can be divided without destruction, are capable of being reproduced in different ways: 1. Because they contain dissimilar particles; 2. Because the form of these bodies is less fixed and determined than that of an animal, diffe|rent parts may supply the functions of each o|ther,

and vary according to circumstances: The roots of a tree, when exposed to the air, push out branches and leaves; and thus the organic par|ticles of vegetables obtain a local establishment, become fixed, and produce individuals in many different ways.

The same phaenomenon is exhibited in ani|mals whose organization is less perfect, as in the fresh water polypus, and others, that are capable of reproducing by the division of their parts. These organized bodies, instead of single ani|mals, may be considered as bundles of organized beings united by a common membrane, as trees are composed of an infinite number of minute trees* 1.65. The vine-fretters, which propagate indi|vidually, likewise contain dissimilar particles; because, after producing their young, they change into barren flies. Snails mutually com|municate dissimilar particles to each other; and, therefore, each individual is fruitful. Thus, in every mode of generation with which we are acquainted, we find, that the necessary union of the organic particles cannot be effected but by the admixture of different particles, to serve as a common basis, and to fix or destroy their ac|tivity.

According to this general idea of sexes, we may suppose, that the distinction of sex extends through all Nature; for sex, in this sense, is no|thing but that part of bodies which furnishes

organic particles of a different kind from those of the common parts, and which serve as a basis for their union. But it is, perhaps, useless to reason on a question which can be solved at once, by saying, that, as God has created sexes, ani|mals must necessarily be produced by their in|tervention. We are not in a condition, as I formerly remarked, to explain why things exist; we are unable to explain why Nature almost universally employs sexes for the reproduction of animals, or why sexes exist. We ought, therefore, to content ourselves with reasoning concerning things as they are. If we attempt to rise higher, we lose ourselves in the regions of fancy, and forget the narrow limits of our knowledge.

Leaving, therefore, all farther subtleties, I shall adhere to nothing that is not founded on facts and observation. I find that the repro|duction of bodies is effected in many different modes: But, at the same time, I clearly perceive, that animals and vegetables are reproduced by the union of the organic particles detached from all parts of their bodies. I am certain that these active organic particles exist in the seeds of ve|getables, and in the seminal fluids of animals, both male and female; and have no doubt that every species of reproduction is accomplished by the union and admixture of these particles. It is equally unquestionable, that, in the gene|ration of man, and other animals, the organic

particles of the male and female mix at the time of conception; because we often see children who resemble both father and mother: And, what confirms this theory is, that all the particles common to the two sexes mix together promis|cuously, but that the particles peculiar to the sexes never mix; for we daily perceive children with eyes resembling those of the father, while their mouth and front resemble those of the mother. But we never see any such mixture of resemblances in the sexual parts; we never find, in the same individual, the testicles of the father and the vagina of the mother.

The formation of the foetus, therefore, is ef|fected by the mixture of the organic particles of both sexes; and this mixture fixes or gives a lo|cal establishment to the particles, because it is made according to the laws of affinity which take place between the different parts, and which determine the particles to arrange themselves in the same order they observed when they existed in the individuals who furnished them. The particles which proceed from the head, for ex|ample, cannot, according to these laws, take up their station in the legs, or in any other part but the head of the foetus. All the particles are in motion when they first unite; and this mo|tion must be round the point or centre of union. This basis or central point, which is necessary to the union of the particles, and which, by its reaction and inertia, fixes and destroys their ac|tivity,

is probably the first assemblage of parti|cles that proceed from the sexual parts, because they are the only particles in the mixture that differ from those common to both sexes.

I imagine, therefore, that, in the mixture of the two fluids, the organic particles which come from the sexual parts of the male fix themselves first, and cannot unite with those which pro|ceed from the seminal parts of the female, be|cause they are of a different nature, and have less affinity to each other than the particles that come from the eye, the arm, or any other part of the female. Round this centre, or point of union, the other organic particles successively ar|range themselves in the same order they former|ly existed in the body from which they were de|rived; and, according as the particles of the one or of the other individual most abound, or near|er this central point, they enter in greater or less quantities into the composition of the new being, which, in this manner, is formed in the middle of a homogeneous fluid; at the same time, vessels begin to shoot, which increase in proportion to the growth of the foetus, and fur|nish it with proper nourishment. These vessels, which have a peculiar species of organization, are probably formed by the excess of the orga|nic particles which have not been admitted into the composition of the foetus; for, as these particles are both active, and furnished with a base or point of union from the organic particles pecu|liar

to the sexual parts of the other individual, they must arrange themselves in the form of an organized body, but not in the form of another foetus; because their position with respect to each other has been changed by the different movements of the particles which entered into the composition of the first foetus. From the union of these superabundant particles, therefore, an irregular body must arise, which will resemble the foetus in nothing but its growth and expan|sion; because, though this body be composed of the same organic active particles with the foetus, their position and form must be different, as they were thrown aside from the centre or point of union, which served as a basis for the formation of the foetus.

When the quantity of seminal fluid of both individuals is great, or, rather, when these liquors abound with organic particles, different centres of attraction are formed in different parts of the mixture; and, in that case, by a mechanism si|milar to what has been mentioned above, several foetuses are formed, some of them males, and others females, according as the particles of the one sex or of the other are most active. But, from the same centre of attraction, two foetuses can never originate; because two centres are re|quisite for this purpose. Besides, if this were to happen, no particles would be left for the for|mation of the placenta and membranes; because they would all be employed in constituting the

second foetus, which would necessarily be a fe|male, if the other was a male. All that could happen in such a case would be, that some of the particles common to both individuals, being equally attracted by the first centre of union, must arrive there at the same time, and produce a monster, or a foetus with superfluous parts; or, if some of the common particles should fix at too great a distance from the first centre, or be constrained by the attraction of the second, round which the placenta is formed, a monster, defec|tive in some part, would be the consequence.

That the organic particles peculiar to the sex|ual parts serve for a basis or centre of union to the other particles of which the embryo is form|ed, I pretend not to demonstrate: But, as they are the only particles which differ from the rest, it is more natural to imagine that they should answer this purpose than those which are com|mon to both individuals.

I formerly detected the errors of those who maintained, that the heart, or the blood, were first formed. The whole is formed at the same time. We learn from actual observation, that the chicken exists in the egg before it is sit upon. The head, the back-bone, and even the appen|dages which form the placenta, are all distinguish|able. I have opened a great number of eggs, both before and after incubation, and I am con|vinced, from the evidence of my own eyes, that the whole chicken exists, in the middle of the

cicatrice, the moment the egg issues from the bo|dy of the hen. The heat communicated to it by incubation, only expands the parts, by putting the fluids in motion. But we have never been able to determine, with certainty, what parts of the foetus are first fixed, at the moment of its formation.

I have always maintained, that the organic particles were fixed, and that they united in con|sequence of their motion being suspended. Of the truth of this fact I am fully convinced; for, if the male and female semen be separately exa|mined, we find in both a great number of mo|ving particles; but, when these fluids are mix|ed, the motion of the particles is totally destroy|ed, and a certain degree of heat is necessary to renew their activity; for the chicken, which ex|ists in the centre of the cicatrice, has no motion before incubation; and, even 24 hours, or two days afterwards, when we begin to perceive it without the microscope, it has not the smallest appearance of motion. During the first two or three days, the foetus is only a small white mu|cilaginous mass, which gradually acquires con|sistence and magnitude. But this progress is ex|ceedingly slow, and has no resemblance to the rapid movements of the organic particles in the seminal fluid. Besides, it was not without rea|son that I maintained that the motion of the or|ganic particles was entirely destroyed; for, if eggs be kept without exposing them to the de|gree

of heat that is necessary for the expan|sion of the chicken, the embryo, though com|pleatly formed, will remain without any motion, and the organic particles of which it is compo|sed will continue fixed, without being able to give life and motion to the embryo which was formed by their union. Thus, after the motion of the organic particles is stopped, and after they have united in such a manner as to form a foe|tus, some external cause is still necessary to give them life and motion. This cause, or agent, is heat, which, by rarifying the fluids, obliges them to circulate: This circulation makes all the or|gans act; and nothing farther is necessary for the growth and expansion of the parts than the continuation of this heat.

Before the action of this external heat, there is not the smallest appearance of blood; and I never could perceive any change of colour in the vessels till about 24 hours after incubation. In the vessels of the placenta, which communi|cate with the body of the foetus, the blood first appears. But, it would seem that this blood lo|ses its red colour, as it approaches the body of the animal; for the chicken is entirely white; and, during the first, second, and third days af|ter incubation, we can with difficulty perceive a few red particles near the animal's body, but which seem not to make any part of it, though these red particles are destined for the formation of the heart. Thus the formation of blood is an effect produced by the motion communicated

to the fluids by heat; and even this blood is formed without the body of the animal, the whole substance of which consists of a white mucilage.

The foetus, as well as the placenta, receive the nourishment that is necessary for their expansion by a species of absorption; and they assimilate the organic particles of the liquor in which they swim: For, it is an equal impropriety to say that the placenta nourishes the animal, as that the a|nimal nourishes the placenta. If the placenta nourished the foetus, the former would diminish in proportion to the growth of the latter, which by no means happens; for both augment toge|ther. I have indeed observed, that, in eggs, the placenta at first grows much more in proportion than the foetus, and, consequently, it may nou|rish the animal; or, rather, it conveys nourish|ment to it by means of absorption.

What we have said concerning the chicken, admits of an easy application to the human foe|tus, which is formed by the union of the orga|nic particles of the two sexes. The membranes and placenta are produced by the superabundant particles that enter not into the composition of the foetus, which is now inclosed in a double membrane, containing also a quantity of fluid. This fluid is at first, perhaps, nothing but a por|tion of the seminal liquors of the father and mo|ther; and, as the foetus is not thrown out of the uterus, it enjoys, from the moment of its forma|tion,

as much external heat as is sufficient for its expansion. This heat communicates motion to the fluids; it gives play to all the organs; and the blood is formed in the placenta, and in the body of the foetus, solely by the motion excited by the heat. We might even maintain, that the formation of the blood in a child is as indepen|dent of the mother, as that which arises in the egg is independent of the hen that covers it, or of the furnace which heats it.

It is certain that the foetus, the membranes, and the placenta, are all nourished and expanded by absorption; for, at first, the sack that con|tains the whole product of generation does not adhere to the uterus: And we have seen, from the experiments of De Graaf upon female rab|bits, that he made the globules which contained the foetuses roll about in the uterus. They could receive no nourishment, therefore, but by absorbing the fluids that constantly bedew the uterus, to which they afterwards begin to ad|here by means of a mucilage that gradually gives origin to small blood-vessels, as shall afterwards be more fully explained.

But to return to the formation of the foetus, concerning which we have to make several re|marks, both as to its situation, and to the differ|ent circumstances that may prevent or alter the mode of its production.

In the human species, the semen of the male enters into the uterus, the cavity of which is

considerable; and, when it meets with a suffi|cient quantity of female semen, the two instantly mix, and the organic particles unite and form the foetus. The whole is, perhaps, performed in a moment, especially if the two fluids be in an active state. The cavity of the uterus is the proper place for the formation of the foetus; because the semen of the male has an easier ad|mission into the uterus than into the Fallopian tubes or ovarium; and, as the uterus has only a small aperture, which is always shut, excepting when opened by the ardor of love, the materi|als of generation remain there in safety, unless they be disturbed by some rare and accidental circumstance. But, as the male fluid moistens the vagina, before it penetrates the uterus, and, as the organic particles are exceedingly active, it may penetrate as far as the Fallopian tubes and ovarium. In the same manner, as the fe|male fluid is already perfected in the glandular bodies of the testicles, from which it distills and moistens the Fallopian tubes, before it descends into the uterus; and, as it may escape through the lacunae round the neck of the uterus, it is not impossible that the mixture of the two li|quors may take place in all these different pla|ces. Foetuses, therefore, may frequently be formed in the vagina, and instantly fall out of it, having nothing proper for their retention. They may also be sometimes formed in the Fal|lopian

tubes; but instances of this kind must be rare.

Anatomists mention, that foetuses have been found, not only in the Fallopian tubes, but like|wise in the ovaria. M. Theroude* 1.66, a surgeon in Paris, showed to the academy a rude mass which he found in the right ovarium of a girl of 18 years of age. Two open fissures, garnished with hair like the eye-lids, were perceived in it. Above these eye-lids was a kind of front, with a black line in place of eye-brows. Immediate|ly above the front, there were several hairs col|lected into two separate pencils, one of them a|bout seven inches long, and the other three. Below the angle of the eye, two large, hard, white dentes molares appeared, together with their gums: These teeth were about three lines long, and about a line distant from each other. Se|veral other teeth appeared, situated at different distances. In the same volume* 1.67, M. Mery is reported to have found in the ovarium of a wo|man an upper jaw-bone, with several teeth in it, so perfect that they appeared to be at least of ten years growth. In the Medical Jour|nal, published by the Abbé de la Roque* 1.68, we have the history of a woman, who died of her ninth child, which had been formed in or near one of the ovaria; for, from the description, it is not clear whether the child was within the o|varium,

or only adjacent to it. This foetus was about an inch thick, and compleatly formed. In the Philosophical Transactions, examples are re|corded of teeth, hair, and bones being found in the ovaria of women. If all these facts can be credited, the seminal liquor of the male must be supposed sometimes, though rarely, to mount up to the ovaria. But there are many considerations which render this point extremely doubtful: 1. The facts which seem to support it are few: 2. The only instance of a perfect foetus found in the ovarium, is narrated in a very suspicious manner by M. Littre. Neither is it impossible that the seminal fluid of the female alone may sometimes produce organized masses, as moles, cists full of hair, of bones, or of flesh. Besides, if we are to believe anatomists, foetuses may be formed in the testicles of men as well as in those of women; for, we are told by a surgeon, in the 2d volume of the history of the old academy* 1.69, that he found a foetus, with its membranes, in which the head, the feet, the eyes, the bones and cartilages, were distinguishable in the scrotum of a man. Were all these facts equally worthy of credit, we must necessarily adopt one of the two following hypotheses; either that the seminal fluid of each sex can produce nothing without being mixed with the other; or, that either of the fluids alone is capable of producing irregu|larly organized masses. If we maintain the for|mer

hypothesis, to explain the facts above rela|ted, we shall be obliged to admit, that the male fluid sometimes ascends to the ovarium, and, by mixing there with the female fluid, forms or|ganized bodies; and also, that the female fluid, by being copiously effused in the vagina, may, in the time of coition, penetrate as far as the scrotum of the male, in the same manner as the venereal virus often reaches that part; and, con|sequently, that an organized body may be form|ed in the scrotum by a mixture of the male and female fluids. If the other hypothesis, which is the most probable, be adopted, namely, that the seminal fluid of each individual may separately produce organized masses, then all these osseous, fleshy, and hairy bodies, which sometimes appear in the ovaria of females, and in the scrotum of males, may derive their origin from the seminal fluid of the individual in which they are found. But it is needless to speculate farther concerning facts which seem to be more uncertain than in|explicable; for I am inclined to think, that the seminal fluid of each individual may singly pro|duce something; and that young girls, for ex|ample, may produce moles, without any inter|course with the male, in the same manner as hens lay eggs without the intervention of the cock. I might support this opinion with obser|vations equally credible as those we have just now quoted. M. de la Saone, a physician and anatomist, published a treatise on this subject, in

which he assures us, that nuns, though strictly cloistered, sometimes produce moles: And why should this be impossible, since hens produce eggs without any communication with the cock, and since we find, in the cicatrices of these eggs, in|stead of a chicken, a mole with its appendages? The analogy here is sufficiently strong to make us at least suspend a rash determination. What|ever be in this, it is certain, that a mixture of the two fluids is necessary for the formation of a foetus, and that this mixture cannot be pro|perly effected but in the uterus, or in the Fallo|pian tubes, where anatomists have sometimes dis|covered foetuses: And it is natural to imagine, that those which have been found in the cavity of the abdomen, have escaped by the extremity of the tube, or by some accidental rupture of the uterus; and that they never fall into the abdo|men from the ovarium, because I think it next to impossible that the seminal fluid should ascend so far. Leeuwenhoek has computed the motion of his pretended spermatic animals to be four or five inches in 40 minutes; so that, if the whole fluid moved at this rate, in an hour or two the animalcules might proceed from the va|gina into the uterus, from the uterus into the Fallopian tubes, and from the Fallopian tubes into the ovaria. But, how is it possible to con|ceive, that the organic particles, whose motion ceases whenever they are deprived of the fluid part of the semen, should arrive at the ovarium,

unless they were accompanied with the liquor in which they swim? The moving particles cannot give a progressive motion to the fluid which contains them. Thus, whatever activity may be ascribed to these organic particles, we cannot conceive how they should arrive at the ovarium, and there form a foetus, unless, by some unknown power, the fluid is absorbed by the ovarium, a supposition which is not only gra|tuitous, but contrary to probability.

The difficulty attending this supposition con|firms the opinion, that the male fluid enters the uterus, either by its orifice, or by penetrating its substance. The female fluid may likewise find its way into the uterus, either by the aperture at the extremity of the Fallopian tubes, or by pe|netrating the substance of the tubes and uterus. M. Weitbrech, an able anatomist of the acade|my of Petersburg, has clearly proved that the se|minal fluid can penetrate through the substance of the uterus: 'Res omni attentione dignissima,' says he, 'oblata mihi est in utero feminae alicu|jus a me dissectae; erat uterus ea magnitudi|ne qua esse solet in virginibus, tubaeque ambae apertae quidem ad ingressum uteri, ita ut ex hoc in illas cum specillo facile possem transire ac flatum injicere, sed in tubarum extremo nul|la debatur apertura, nullus aditus; fimbriarum enim ne vestigium quidem aderat, sed loco il|larum bulbus aliquis pyriformis materia subal|bida

fluida turgens, in cujus medio fibra plana nervea, cicatriculae acmula, apparebat, quae sub ligamentuli specie usque ad ovarii involu|cra protendebatur.'

'Dices, eadem a Regnero de Graaf jam olim notata. Equidem non negaverim illus|trem hunc prosectorem, in libro suo de organis mulieribus, non modo similem tubam delineasse, Tab. xix. sig. 3. sed et monuisse "tubas, quam|vis, sccundum ordinariam naturae dispositionem, in extremitate sua notabilem semper coarcta|tionem habeant, practer naturam tamen ali|quando claudi;" verum enimvero cum non meminerit auctor an id in utraque tuba ita de|prehenderit, an in virgine, an status iste prae|ternaturalis sterilitatem inducat, an vero con|ceptio nihilominus fieri possit, an a principio vitae talis structura suam originem ducat, sive an tractu temporis ita degenerare tubae possint, facile perspicimus multa nobis relicta esse pro|blemata, quae, utcumque soluta, multum nego|tii facescant in exemplo nostro. Erat enim haec foemina maritata, viginti quatuor annos nata, quae filium pepererat quem vidi ipse, octo jam annos natum. Dic igitur tubas ab incun•••••…•••••… clausas sterilitatem inducere: Quare haec nostra foemina peperit? Dic concepisse 〈…〉〈…〉: Quomodo ovulum ingredi tubam potuit? Dic ••••aluisse tubas post partum: Quomodo id nost•••• quomodo adeo evanescere in

utroque latere fimbriae possunt, tanquam nun|quam adfuissent? Si quidem ex ovario ad tu|bas alia daretur via, praeter illarum orificium, unico gressu omnes superarentur difficultates; sed fictiones intellectum quidem adjuvant, rei veritatem non demonstrant; praestat igitur ig|norationem fateri, quam speculationibus in|dulgere* 1.70.' These difficulties, which occurred to this acute observer, are insurmountable, accor|ding to the ovicular system. But the fact he re|cords is alone sufficient to demonstrate, that the female fluid may penetrate the substance of the uterus; and it is not to be doubted that the male fluid is capable of entering it in the same man|ner. The change which the male fluid produ|ces in the uterus, and the species of vegetation or expansion which it occasions in that viscus, is sufficient to demonstrate the truth of the fact. Besides, the fluid which issues through the la|cunae of De Graaf being of the same nature with that of the glandular bodies, it is evident that this liquor proceeds from the ovaria; and yet there are no vessels through which it could pass. We must therefore conclude, that it pene|trates through the spongy substance of the parts, and that it not only enters the uterus, but may even issue out of it, when the parts are irritated.

But, though this penetration should be re|garded as impossible, it cannot be denied, that the female fluid, which distills from the glandu|lar

bodies of the ovaria, may fall into the uterus, by entering the apertures at the extremities of the Fallopian tubes, as the male fluid enters by the orifice of the uterus itself; and, consequent|ly, that the foetus may be formed in the cavity of the uterus, by the mixture of the two fluids, in the manner already explained.

CHAP. XI.

Of the Expansion, Growth, and Delivery of the Foetus, &c.

IN the expansion of the foetus, two different species of growth are distinguishable: The first, which immediately succeeds the formation of the foetus, is not uniform in all the parts of the animal. The nearer the foetus approaches to maturity, the growth of the parts is more proportional; and it is not till after the birth, that all the parts grow nearly in an equable manner. We must not imagine, that the foe|tus, at the time of its formation, has the exact figure of an adult. The small embryo, it is true, contains all the parts essential to a man; but they differ in their successive expansion.

In an organized body, like that of an animal, some parts may be supposed to be more essential than others; and though none of them are use|less or superfluous, yet there are some to which others seem to owe their growth and disposition. Some parts may be considered as fundamental, without which the animal could not exist, and others as only superficial and accessory. The

latter seem to derive their origin from the for|mer, and to be intended more for conferring symmetry and external ornament on the animal, than for enabling it to exist, or to perform the functions essential to life. These two different species of parts are successively expanded, and are almost equally apparent at the time of birth. But there are other parts, as the teeth, which arrive not at full maturity till several years af|ter; and others, as the glandular bodies in the female testicles, the beard of males, &c. which appear not till the age of puberty.

To discover the fundamental and essential parts of an animal body, attention must be had to the number, situation, and nature of the whole. Those which are simple, those whose position is invariable, and those without which the animal cannot exist, must necessarily be the most essential. Those, on the contrary, which are double, or more numerous, those which vary in size and position, and those which may be taken away without injuring or killing the creature, may be regarded as less essential, or more accessory to the animal machine. Aristotle mentions, that the only parts essential to all ani|mals are those with which they take and digest their nourishment, and throw out the superflu|ous part of it from the body. The whole in|testinal canal is indeed extremely simple, and no other part can supply its place. The head and back-bone are likewise simple parts, the po|sition

of which is invariable. The back-bone is the foundation of the animal frame; and the action and movements of most members of the body depend upon the spinal marrow which that bone contains. It is this part, also, together with the head, which appears first in the embryo. Now, these simple parts, which are first formed, are all essential to the existence and the form of the animal.

The double parts in an animal body are more numerous than the single parts; and they seem to be produced on each side of the single parts by a species of vegetation; for the double parts are similar in form, and different only in position. The left hand is perfectly similar to the right; but, if the left hand was placed in the situation of the right, we could not perform the same ac|tions with it. The same thing may be observed of all the double parts: They are similar in form, but differ in position, which is relative to the body of the particular animal; and, if a line were drawn, dividing the body into two equal parts, the position of all the similar parts would tend to this line as to a centre.

The spinal marrow, and the vertebrae in which it is inclosed, appear to be the real axis of all the double parts of the animal body, from which they seem to derive their origin, and to be only proportional branches issuing from this trunk or common base; for, in the young chick, we see the ribs shooting from each side of the

vertebrae, as the small branches shoot out from the principal branch of a tree. In all embryos, the middle of the head and the vertebrae first appear; we then see, on each side of the vesicle which composes the middle of the head, two o|ther vesicles which seem to proceed from the first: These two vesicles contain the eyes, and the other double parts of the head. In the same manner, we perceive an equal number of small tubercles issuing from each side of the vertebrae, which gradually extend, and form the ribs, and other double parts of the trunk. Lastly, the arms and legs appear like small tubercles on each side of the trunk. This first growth is very different from what afterwards takes place: It is the production of parts which appear for the first time; the growth which succeeds is on|ly an expansion of parts already formed.

The order and symmetry of the double parts in all animals, their regular position, the equa|lity of their extension and growth, and the per|fect similarity of their structure, seem to indi|cate, that they derive their origin from the sin|gle parts; that a certain force resides in the sin|gle parts that acts equally on each side; or, which amounts to the same, they are the bases or fulcra against which the action of those powers that produce the expansion of the double parts is exerted; and that the action of these forces, both on the right and left sides, are precisely equal, and counterbalance each other.

Hence we may conclude, that, if there is any defect, or redundance, in the matter destined for the formation of the double parts, as the forces are equal on each side, this defect or excess must take place both in the right and left sides. If, for example, from a defect of matter, a man has but two fingers in the right hand, in place of five, the same defect will appear in the left; if, from an excess of matter, there be six fingers in the right hand, he will have the same number in the left; or, if the matter be vitiated, and produces a change in the parts of one side, the same change will appear in the other. Of this fact we have daily proofs: The parts of monsters are always deranged in a certain order and proportion. Hence Nature, even in her er|rors, uniformly commits the least of possible mistakes.

This harmony in the position of the double parts of animals, is likewise apparent in vege|tables. The branches push out smaller ramifi|cations on each side; the small nerves in the leaves are equally disposed with regard to the principal nerve; and, if the symmetry appears to be less exact in vegetables than in animals, this proceeds only from its being more various, and because its limits are more extensive, and less precise. But the same order is easily recog|nisable; and the single and essential parts are perfectly distinct from those which are double;

and it is evident, that the latter derive their ori|gin from the former.

It is impossible to determine the form of these double parts before their expansion, or in what manner they are complicated, or what figure results from their position in relation to the single parts. The body of an animal, at the instant of its formation, unquestionably con|tains all the parts of which it ought to be com|posed: But the relative disposition of these parts is then very different from what after|wards appears. If we examine the expansion of a young leaf of a tree, we will find that it is plaited on each side of the principal nerve; and that its figure, at this time, has no resemblance to that which it afterwards assumes. When we amuse ourselves with plaiting paper, in order to give it the form of a crown, of a boat, &c. the different plaits of the paper seem to have no re|semblance to the figure which results from their expansion: We only perceive that the plaits are uniformly made in a certain order and pro|portion, and that, whatever is done on one side, is also done on the other. But, to determine the figures which may result from the expan|sion of any given number of folds, is a problem beyond the powers of geometry. The science of mathematics reaches not what immediately depends upon position. Leibnitz's art of Ana|lysis situs does not yet exist; though the art of knowing the relations that result from the posi|tion

of things would be, perhaps, more useful than that which has only magnitude for its ob|ject; for we have more occasion to be acquaint|ed with form than with matter.

In the expansion of natural productions, the folded or plaited parts not only assume different positions, but they acquire, at the same time, ex|tension and solidity. Since, therefore, we are unable to ascertain the exact result of a simple expansion of a folded figure, in which, as in folded paper, nothing takes place but a change of position among the parts, without any aug|mentation or diminution of the quantity of matter, how is it possible for us to judge con|cerning the expansion of the compound body of an animal, in which not only the relative posi|tion, but likewise the quantity of matter in these parts, suffer considerable changes? We can only reason, therefore, on this subject, by drawing conclusions from the examination of objects at different periods of their expansion.

We, indeed, perceive the chick in the egg before incubation: It swims in a transparent fluid, contained in a small purse formed by a very fine membrane in the centre of the cica|trice. But the chick is then only a particle of inanimated matter, in which no organization or determined figure can be distinguished. We can perceive, however, that one of its extremities is the head, and the other the back-bone. The embryo, in this state, seems to be the first pro|duct

of fecundation, resulting from the mixture of the male and female semen. To ascertain this fact, several things require attention: When the hen has, for some days, been along with the cock, and afterwards separated from him, the eggs produced 20 days or a month after this se|paration, are equally fertile as those laid during her cohabitation with the male. The eggs pro|duced at the end of this period require only the usual time of 21 days in hatching; and their embryos are equally advanced both in form and consistence. From this circumstance we might be led to imagine, that the form in which the embryo appears before incubation, is not the immediate effect of the mixture of the two se|minal fluids, but that it existed in different forms during the abode of the egg in the body of the mother; for the embryo, in the form in which we see it before incubation, requires only the aid of heat in order to bring it to maturity. Now, if this form of the embryo had existed 21 days or a month before, when the egg was first impregnated, why was it not hatched by the internal heat of the mother? Why do we not find the chick compleatly formed in those eggs which have been impregnated 21 days be|fore they are laid?

But this difficulty, though seemingly great, is not insurmountable. When the hen cohabits with the cock, the cicatrice of each egg, which contains the semen of the female, receives a small

quantity of the male fluid. The eggs in the o|varium of oviparous females are analogous to the glandular bodies in the testicles of the vivipa|rous: The cicatrice of the egg corresponds to the cavity of those glandular bodies which con|tain the female semen; and that of the male pe|netrates and mixes with it. The formation of the embryo instantly results from this mixture or union of the two fluids. The first egg laid by the hen after her communication with the cock, is fecundated and capable of being hatch|ed. Those which she is afterwards to lay were all impregnated at the same instant: But, as they want some essential parts, the production of which has no dependence on the male fluid; as they have neither the white, the membranes, nor the shell, the small embryos contained in the cicatrices of these imperfect eggs, are inca|pable of being hatched, though aided by the in|ternal heat of the mother. The embryo, there|fore, remains in the cicatrice, in the same state in which it was first formed, till the egg acquires all the parts necessary to the growth and nou|rishment of the foetus; and it is not till after the egg has arrived at full perfection, that the ex|pansion of the embryo commences. This ex|pansion is effected by the external heat of incu|bation: But it is unquestionable, that, if the egg could be retained in the body 21 days after it was completely formed, the chick would be hatched, unless the internal heat of the mother

was too great; for the degrees of heat necessa|ry for hatching eggs are very limited; and the least excess or defect is equally fatal to this ope|ration. The last eggs, therefore, laid by the hen, containing the embryos in the same state as the first, prove nothing more than the necessi|ty of their acquiring full perfection before they can be hatched.

It is apparent, therefore, that the state of the embryo when the egg is laid by the hen, is its first state, and that which immediately succeeds impregnation; that it undergoes no interme|diate changes of form; and consequently, by tracing, as Malpighius has done, its gradual ex|pansion, hour after hour, we discover every thing that it is possible for us to know, unless we could perceive the mixture of the two fluids, and the manner in which the particles arrange themselves during the first formation of the em|bryo.

If we reflect on this instantaneous fecundation of a number of eggs, which are to be laid at succes|sive intervals, we shall discover a new argument against the existence of eggs in viviparous ani|mals: For, if women contained eggs, like hens, why are not many of them fecundated at the same time? Why does not one impregnation give birth to a successive race of children? And, when women conceive two or three children, why do they always come into the world at the same time? If these foetuses were produced

from eggs, would they not succeed each other according to the different states of perfection of the several eggs at the time of impregnation? And, would not superfoetations be as frequent as they are rare, and as natural as they are acci|dental?

It is impossible to trace the gradual expansion of the human foetus, as we can that of the chick in the egg. The opportunities for observation are few; and all we know of this subject is de|rived from the writings of anatomists, surgeons, and accoucheurs. It is from collecting all their particular observations, and comparing their re|marks with their descriptions, that the following abridged history of the human foetus has been compiled.

Immediately after the mixture of the two se|minal fluids, it is probable that the whole mate|rials of generation exist in the uterus under the form of a small globe; for we learn from ana|tomists, that, three or four days after conception, there is a small globular mass in the uterus, the greatest diameter of which is about 6 lines, and the least 4. This globe is formed by a de|licate membrane, which contains a limpid li|quor very like the white of an egg. We may already perceive, in this liquor, some small fi|bres, which are the first rudiments of the foetus. Upon the surface of the globe there is a net|work of delicate fibres, which extends from one

of the extremities to the middle: These are the first vestiges of the placenta.

Seven days after conception, the lineaments of the foetus are distinguishable by the naked eye. They are, however, very imperfect, and have the appearance of a gelly almost transparent, though it has acquired some degree of solidity. The head and trunk may be easily distinguish|ed; because this mass is of an oblong figure, and the trunk is longest and most delicate. Some small fibres, resembling a plume of feathers, is|sue from the middle of the foetus, and termi|nate in the membrane in which it is inclosed. These fibres are the rudiments of the umbilical cord.

Fifteen days after conception, the head and the most prominent features of the face are ap|parent. The nose resembles a small elevated thread perpendicular to a line which marks the di|vision of the lips: Two small black points repre|sent the eyes; and we see two holes in place of ears. The body of the foetus has also acquired some growth. On each side of the superior and in|ferior parts of the trunk, those small protube|rances appear, which are the rudiments of the arms and legs. The length of the whole body is about five French lines.

Eight days after, in all three weeks, the body of the foetus is only augmented about a line: But the arms and legs are apparent. The growth of the arms is quicker than that of the

legs; and the fingers separate sooner than the toes. The internal organization now begins to be visible: The bones appear like fine threads. The ribs are disposed on each side of the back-bone like minute threads: The arms, the legs, the fingers and toes, are also represented by si|milar threads.

At one month, the foetus is more than an inch in length: It naturally assumes a curved posture in the middle of the liquor that sur|rounds it; and the membranes in which the whole is included, are both augmented and thickened. The whole mass is of an oval figure, the greatest diameter of which is about an inch and a half, and the least about an inch and a quarter. The human figure is no longer equi|vocal: All the parts of the face are already distinguishable; the body is delineated; the haunches and the belly are prominent; the hands and legs are formed, and their fingers and toes are divided; the skin is thin and transpa|rent; the viscera resemble a knot or plexus of sibres; the vessels are like fine threads, and the membranes are extremely delicate: The bones are still soft, and it is only in a few places that they have begun to assume some degree of soli|dity. The vessels which form the umbilical cord lie parallel to each other in a straight line. The placenta now occupies only a third of the whole mass, instead of a half, which it did during the first days; the superficial growth of the placenta,

therefore, has not been so great as that of the foetus and mass; but it has received a great augmentation in solidity; it has become pro|portionally thicker than the membranes of the foetus, both of which are now distinguishable.

According to Hippocrates, the male foetus expands sooner than the female.

At the end of six weeks, the foetus is about two inches long, and the human form begins to be more perfect, only the head is very large in proportion to the other parts of the body. A|bout this time the motion of the heart becomes visible: In 50 days, the heart has been percei|ved to beat for a considerable time after the foetus was extracted from the uterus.

In two months, the foetus is more than two inches in length; and the ossisication is per|ceptible in the middle of the two arm-bones, in the thigh and leg, and in the point of the under jaw, which is then greatly advanced before the upper. These, however, are only osseous points. But, by means of a quicker growth, the clavi|cles are entirely ossified: The umbilical cord is formed, and the vessels which compose it begin to twist like the threads of a rope: But this cord is very short in comparison of the length it afterwards acquires.

In three months, the foetus is nearly three inches long, and weighs about three ounces. Hippocrates asserts, that at this time the motions of the male foetus begin to be felt by the mo|ther;

but that those of the female are not per|ceptible till four months. Some women, how|ever, affirm that they have felt the motions of the foetus at the beginning of the second month. It is difficult to acquire any certain knowledge on this subject: The sensations excited by the first movements of the foetus depend more, per|haps, on the sensibility of the mother, than the strength of the child.

Four months and a half after conception, the length of the foetus is from six to seven inches. All the parts are greatly augmented, and easily distinguishable from each other: Even the nails appear on the fingers and toes. The testicles of the male are shut up in the belly above the kid|neys. The stomach is filled with a thick fluid, similar to that which is contained in the amnios. In the small guts we find a milky fluid, and a black liquid matter in the great guts. There is a small quantity of bile in the vesica felis, and a little urine in the bladder. As the foetus floats freely in the fluid that surrounds it, there is always some space between its body and the membranes in which it is contained. These membranes, at first, grow more rapidly than the foetus; but, after a certain time, the reverse takes place. Before the end of the third month, the head is bent forward; the chin rests on the breast; the knees are elevated, and the legs folded back upon the thighs. One of the hands, and often both, touch the face. Afterwards,

when the foetus acquires more strength, it per|petually changes its position, as we learn from the following observations made by persons skil|led in the art of midwisery: 1. The umbilical cord is often twisted round the body and mem|bers of the child, in a manner that necessarily supposes different motions and positions. 2. Mo|thers feel the motion of the child sometimes on one side of the uterus, and sometimes on the o|ther; and it often strikes against many different places, which could not happen unless it assumed different positions. 3. As the foetus swims in a fluid which surrounds it on all sides, it may ea|sily turn, extend, and twist itself by its own powers: It must likewise take different situations, according to the various attitudes of the mo|ther's body; when the mother, for example, lies down, the position of the foetus must differ from what it is when she stands.

Most anatomists maintain, that the foetus is obliged to bend its body, because it is too much confined by the membranes. But this opinion seems not to be well founded; for, during the first five or six months, at least, there is room more than sufficient to admit a full extension of the foetus; and yet, during all this period, the foetus is bended. We see likewise, that the chick is bended in the liquor of the amnios, while, at the same time, this membrane, and the fluid it contains, afford room sufficient to hold a body five or six times larger than the foetus. We

may, therefore, conclude, that the bended po|sture of the foetus is natural, and not the effect of restraint. I am inclined to think, with Harvey, that the foetus takes this posture, be|cause it is most favourable to rest and sleep; for all animals bend their bodies when they want to repose themselves, or to sleep: And, as the foetus sleeps almost continually, it naturally as|sumes this advantageous position. 'Certe,' says this celebrated anatomist, 'animalia omnia, dum quiescunt et dormiunt, membra sua ut pluri|mum adducunt et complicant, figuramque o|valem ac conglobatam quaerunt: Ita pariter embryones qui aetatem suam maxime somno transigunt, membra sua positione ea qua plas|mantur (tanquam naturalissima ac maxime in|dolenti quietique aptissima) componunt* 1.71.'

The uterus, as formerly remarked, grows very quickly after pregnancy; and it continues to increase proportionally with the foetus. But the growth of the foetus at last exceeds that of the uterus; and it is natural to think, that the foetus, when near maturity, is too much con|fined, and agitates the uterus by repeated mo|tions. The mother feels those successive efforts, which are called periodic pains, after the la|bour of child-bearing commences. The more force the foetus exerts in order to dilate the u|terus, it finds an increased resistance from the natural elasticity of the parts. Hence every ef|fort

tends to open the os tincae, or orifice of the uterus, which has already been gradually en|larged during the last months of pregnancy. The head of the foetus pushes along against the margins of this orifice, and dilates it by a con|stant pressure, till the moment of delivery, when it opens so wide as to allow a free passage to the child.

What renders it probable that the labour|-pains are occasioned by the dilatation of the os tincae is, that this dilatation is the only certain mode of distinguishing the real from the false pains. Women often feel very brisk pains, which are not those that immediately precede delivery. To distinguish those false from the true pains, Deventer advises the accoucheur to feel the orifice of the uterus, and maintains, that, if the pains be true, the dilatation will augment upon the occasion of every pain; and that, on the contrary, if the pains be false, the orifice will rather contract than dilate, or, at least, that it will not continue to dilate. Hence we may conclude, that these pains proceed not from a forced dilatation of the orifice of the uterus. The only thing that is embarrassing, is the alter|nation of pain and of ease experienced by the mother. This circumstance does not perfectly correspond with the cause we have assigned; for the gradual and continued dilatation of an orifice should produce a constant pain, without any intervals of ease. Perhaps the alternations

may be ascribed to the separation of the placen|ta: It adheres to the uterus by the insertions of a number of small papillae. May we not, therefore, suppose that these papillae separate not from their cavities all at once; and that the successive separation of these papillae gives rise, at different intervals, to the fresh accessions of pains? Here the effect perfectly corresponds with the cause; and this conjecture may be sup|ported by another remark: Immediately before delivery, there issues out a viscous whitish li|quor, similar to that which flows from the pa|pillae of the placenta, when torn from the u|terus. It is therefore extremely probable, that this liquor, which issues from the uterus, is pro|duced by the separation of some of the papillae of the placenta.

It sometimes happens, that the foetus escapes from the uterus without bursting the membranes, and, consequently, without discharging the li|quor they contain. This species of birth seems to be the most natural, and is similar to that of most animals. The human foetus, however, commonly pierces the membranes, by the re|sistance it meets with at the orifice of the uterus: And sometimes a part of the amnios, and even of the chorion, is brought away adhering to the head of the child like a cap. As soon as the membranes are pierced or torn, the liquor, which is called the waters, runs out, and, by lubrica|ting the vagina and orifice of the uterus, facili|tates the passage of the child. After the discharge

of the waters, there is sufficient room left in the uterus for the midwife to return the child, when its position is unfavourable to the birth. After the child comes into the world, the delivery is not completed. The placenta and membranes still remain in the uterus; and the child is at|tached to them by means of the umbilical cord: They are easily brought away by the hand of the midwife; and sometimes the weight of the child is sufficient for that purpose. These or|gans, which were necessary to the existence of the foetus, become useless, and even noxious to the child, after its birth. They are, therefore, instantly disengaged from the child's body, by casting a knot on the umbilical cord, about an inch from the navel, and by cutting the cord an inch above the ligature. In six or seven days, the remains of the cord dry up, and fall off close to the navel.

By examining the foetus before birth, we are enabled to form some ideas concerning the me|chanism of its natural functions. There are or|gans necessary to it while in the womb of the mother, but which become useless immediately after birth. The better to comprehend these functions, we must explain more fully the na|ture of these accessory parts, the umbilical cord, the membranes, with the liquor they contain, and the placenta. The umbilical cord, which is attached to the body of the foetus at the navel, is composed of two arteries and a vein: By

these the course of the circulation is lengthened; but the vein is larger than the arteries. At the extremity of the cord, each of these vessels di|vide into an infinite number of ramifications, and extend themselves between two membranes. They set off from the common trunk in such a manner, that the whole ramifications assume a round form, and are distinguished by the name of placenta, because they resemble a cake. The central part of the placenta is thicker than its edges: Its mean thickness is about an inch, and its diameter is eight or nine inches, and some|times more. The external surface of it, which is applied to the uterus, is convex, and the in|ternal surface is concave. The blood of the foetus circulates in the cord and in the placenta. The arteries of the cord proceed from two large arteries in the foetus, and carry the blood through all the arterial ramifications of the pla|centa; and the blood is collected and returned to the foetus by the venous branches of the pla|centa and the umbilical vein.

The concave surface of the placenta is cover|ed with the chorion: Its convex surface is also covered with a soft membrane, which seems to be a continuation of the chorion, and is easily torn; and the foetus is inclosed in the double covering of the chorion and amnios. The figure of the whole is globular; because the intervals between the foetus and membranes are filled with a transparent fluid. This liquor is imme|diately

confined by the amnios, which is the in|ternal membrane: It is thin and transparent, and folds itself round the umbilical cord, at its insertion into the placenta, and continues to co|ver it the whole way to the navel of the foetus. The chorion is the external membrane; it is thick, spongy, and interspersed with blood-ves|sels. It consists of several coats, the outermost of which covers the convex surface of the pla|centa. It sends off duplicatures to cover the papillae, which are inserted into the cavities at the fundus of the uterus, called lacunae. These insertions connect the foetus to the uterus.

Some anatomists have maintained, that the human foetus, like those of certain quadrupeds, was furnished with an allantois, a membrane destined for the reception of the urine; and they have pretended to have discovered it between the chorion and amnios, or in the middle of the placenta, at the root of the umbilical cord, un|der the form of a pretty large bladder; and that it received the urine by means of a long tube which made a part of the cord, and which open|ed at one end into the bladder, and, at the others, into the allantois, answering the same purposes as the urachus in other animals. They acknow|ledge, however, that the urachus of the human foetus is not near so large as in the quadrupeds; but they assert that it is divided into a number of small tubes, and that the urine passes into their cavities.

To these facts are opposed the experience and observation of most anatomists. They seldom find any vestiges of an allantois either between the chorion and amnios, or in the placenta; nor do they perceive any urachus in the umbi|lical cord. A kind of ligament, indeed, runs from the external surface of the bottom of the bladder to the navel; but, when entering the cord, it becomes so delicate as to be almost re|duced to nothing. Neither is this ligament commonly hollow; and we can perceive no cor|responding aperture in the bottom of the blad|der.

The foetus has no communication with the open air; and the experiments made upon the lungs demonstrate that they have never respired; for they sink in water, while those of infants, who have breathed, uniformly swim: The foe|tus, therefore, has no respiration in the womb of the mother; consequently, it can make no sound with its voice, and all the stories of chil|dren groaning and crying before birth must be regarded as fabulous. After the waters run off, however, the air may find admission into the cavity of the uterus, and the child may begin to respire before its birth. In this case, the child may cry, in the same manner as the chick|en cries before the shell of the egg is broken, which it is enabled to do by means of the air lodged in a cavity between the external mem|brane and the shell: This air exists in all eggs,

and is produced by the fermentation of the matters they contain* 1.72.

The lungs of the foetus, having no motion, receive no more blood than is sufficient for their nourishment and growth: Another passage, therefore, is open for its circulation. The blood in the right auricle of the heart, instead of pas|sing into the pulmonary artery, and, after cir|culating through the lungs, returning into the left auricle by the pulmonary vein, passes direct|ly from the right to the left auricle, through an aperture called the foramen ovale, which is in the partition of the heart that separates the two auricles: The blood then enters the aorta, by the ramifications of which it is distributed to every part of the body; it is then taken up by the numerous branches of the veins, which gra|dually unite into one trunk, called the vena cava, that terminates in the right auricle of the heart. The blood contained in this auricle does not all pass through the foramen ovale; part of it e|scapes into the pulmonary artery, but it enters not into the body of the lungs; for there is a communication between the pulmonary artery and the aorta, by an arterial canal which leads immediately from the one to the other. It is by these means that the blood circulates in the foetus, without entering the lungs, which it does in children, in adults, and in all animals who respire.

It has been imagined by some, that the blood of the mother passes into the body of the foetus, by means of the placenta and umbilical cord: They supposed, that the blood-vessels of the u|terus opened into the lacunae, and those of the placenta into the papillae, and that they inoscu|lated with one another. But this opinion is contradicted by experiment. When the arteries of the umbilical cord are injected, the liquor re|turns by the veins, without any of it escaping externally. Besides, the papillae can be drawn out of the lacunae in which they are lodged, without any extravasation of blood either from the uterus or placenta; from both there oozes out a milky matter, which, we have already re|marked, serves for the nourishment of the foe|tus. It is probable that this liquor enters the veins of the placenta in the same manner as the chyle enters the subclavian vein; and the pla|centa, perhaps, performs the office of the lungs in maturating the blood. One thing is certain, that the blood appears much sooner in the pla|centa than in the foetus; and I have often ob|served, in eggs which had been sit upon for a day or two, that the blood appeared first in the membranes, and that their blood-vessels are nu|merous and large, while the whole body of the foetus, excepting the point where these blood-vessels terminate, is only a white transparent matter, in which there is not the least vestige of blood.

It has been imagined that the liquor of the amnios is a nourishment received by the mouth of the foetus. Some have even pretended to have found this liquor in the stomach, and to have seen several foetuses who wanted the um|bilical cord entirely, and others who had only a small portion of it, which had no connection with the placenta. But, in this case, may not the liquor have passed into the body of the foe|tus by the portion of the cord that remained, or even by the navel itself? Besides, other facts may be opposed to these: Foetuses have been found, whose lips were not separated; and o|thers whose oesophagus had no aperture. To reconcile these facts, some anatomists have main|tained, that the aliment passed into the foetus partly by the umbilical cord, and partly by the mouth. But none of these opinions seem to have any foundation. The question is not, how the foetus alone, but how the whole apparatus of generation, receive their growth and nourish|ment? for the placenta, the liquor, and the membranes, increase in bulk as well as the foe|tus; and, consequently, those instruments and canals employed for receiving and transporting nourishment to the foetus, are themselves en|dowed with a species of life. The expansion of the placenta and membranes is equally diffi|cult to conceive as that of the foetus; and, it may be said, with equal propriety, that the foe|tus nourishes the placenta, as that the placenta

nourishes the foetus. At the commencement of growth, the whole mass floats in the uterus, without any adhesion; and, of course, the nou|rishment can only be conveyed by an absorption of the lacteous fluid contained in the uterus. The placenta appears first to attract this fluid, which it converts into blood, and transports by the veins into the foetus. The liquor amnii seems to be nothing but this milky fluid in a purified state, the quantity of which is augmented, by a similar absorption, in proportion to the growth of the membranes; and the foetus probably ab|sorbs this liquor, which seems to be necessary for its growth and nourishment: For, it is worthy of remark, that the foetus, during the first two or three months, contains very little blood: It is as white as ivory, and appears like a conge|ries of lymph somewhat consolidated; and, as the skin is transparent, and all the parts extreme|ly soft, the body of the foetus may be easily pe|netrated by the fluid in which it swims, and thus receive the matter necessary for its growth and expansion. It may indeed be supposed that the foetus afterwards receives nourishment by the mouth; because we find a liquor, similar to that of the amnios, in the stomach, urine in the blad|der, and meconium, or excrement, in the inte|stines; and, as neither urine nor meconium ap|pear in the amnios, it is natural to conclude, that no excrements are voided by the foetus, e|specially as some are born without having the

anus perforated, and yet large quantities of me|conium are found in their intestines.

Though the foetus has no immediate connec|tion with the uterus, but is only attached to it by the small external papillae of the placenta; though it has no communication with the blood of the mother, but, in some measure, is equally independent of her as the egg is independent of the hen which covers it; yet it has been main|tained, that, whatever affects the mother, pro|duces a similar effect upon the foetus, and that the impressions received by the former are com|municated to the sensorium of the latter. To this imaginary influence have been attributed all those resemblances, monstrosities, and peculiar marks which appear on the skin of particular chil|dren. Many of these marks I have examined, and they uniformly appeared to be occasioned only by a derangement in the texture of the skin. Every mark must necessarily have a faint resemblance to something or other: But such resemblances, I am persuaded, depend more on the imagination of those who see them, than up|on that of the mother. On this subject, the marvellous has been pushed to an extreme de|gree. The foetus has not only been said to bear the real representations of the appetites of the mother, but that, by a singular sympathy, the marks which represent strawberries, cherries, &c. assumed a deeper colour during the season of these fruits. A little attention, however, will

convince us, that these changes of colour are more frequent, and that they happen whenever the motion of the blood is accelerated, whether it be occasioned by the heat of summer, or by any other cause. The marks are always either yellow, or red, or black; because the blood gives these colours to the skin when it enters in too great quantities into the vessels. If these marks were occasioned by the appetites of the mother, why are not their forms and colours as various as the objects of her desires? What a multitude of strange figures would be exhibited, if all the whimsical longings of a mother were written upon the skin of the child?

As our sensations have no resemblance to the objects which excite them, it is impossible that desire, fear, horror, or any other passion or emo|tion, can produce real representations of the ob|jects by which they are occasioned. An infant being, in this respect, equally independent of the mother, as the egg is independent of the hen that sits upon it, I should be equally induced to believe, that the imagination of a hen, which saw by accident a cock's neck twisted, should produce wry-necked chickens from the eggs she was hatching, as that a woman, who saw a man broke upon the wheel; should produce, by the mere force of imagination, a child with all its limbs broken.

But, supposing this fact to be well attested, I still maintain that the imagination of the mother

could not be the cause of it: For, what is the effect of horror? An internal movement, or, if you please, a convulsion of the mother's body, which might alternately compress and stretch the uterus. What would be the result of this commotion? Nothing similar to its cause; for, if the commotion was very violent, the foetus might be killed, wounded, or have some of its parts deranged: But how is it possible to ima|gine that this commotion should produce in the foetus any thing similar to the thoughts of the mother, unless we suppose, with Harvey, that the uterus possesses the faculty of conceiving ideas, and of realising them upon the foetus?

But, if the imagination of the mother has no effect upon the foetus, it may still be demanded, Why did this child come into the world with its members broken? Though a direct solution of a fact, which is both extraordinary and uncer|tain, is not to be expected; yet, I think, this question admits of a satisfactory answer. Phae|nomena of the most uncommon kind, and which are but rarely exhibited, as necessarily happen, as those that are usual and frequent. Among the infinite combinations of which matter is ca|pable of forming, arrangements of the most pe|culiar and extraordinary species must sometimes take place. Hence, out of the numberless chil|dren which daily come into the world, one may sometimes appear with two heads, with four legs, or with all its members broken. It is,

therefore, within the circle of nature, that a child, without the aid of the mother's imagina|tion, may be born with its arms and legs bro|ken. This phaenomenon may have been exhi|bited oftener than once; the mother of this child may, during her pregnancy, have seen a man broken on the wheel; and the defects of conformation in the child may have been attri|buted to the impulse made, by this dreadful spectacle, upon the imagination of the woman. But, independent of this general solution, the fact may be explained in a more direct manner. The foetus, as formerly remarked, has nothing in common with the mother. Its functions, its organs, its blood, its movements, are all peculiar, and belong to itself alone. The only matter it derives from the mother, is the liquor or nutri|tive lymph which distills from the uterus. If this lymph suffers any change, if it be infected with the venereal virus, the infant is affected with the same disease; and it is reasonable to think that all the diseases which proceed from viciated humours may be communicated from the mother to the child. We know that the small pox is communicated in this manner; and we have too many examples of children, imme|diately after birth, becoming innocent victims of the debauchery of their parents. The veneral virus attacks the most solid parts of the bones; and it appears to act with more force upon the middle of the bones, which is the part where the

ossification first commences, and is, of course, the most hard and solid part. I conceive, there|fore, that the infant in question has been affect|ed with the venereal disorder while in the womb of its mother, and that this was the reason why it came into the world with its bones broken through the middle.

The same effect might be produced by the rickets: In the royal cabinet, there is a skeleton of a rickety child, the bones of whose legs and arms are joined in the middle by a callus: From inspecting this skeleton, it appears that its bones had been broken before birth, and afterwards re|united by a callus.

But we have dwelt too long upon a fact which credulity alone has rendered marvellous. Pre|judice, especially that species of it which is founded in wonder, will always triumph over reason. It is needless to attempt to persuade women that the marks on their children have no connection with their ungratified longings. I have sometimes asked them, before the birth of a child, of what particular longings they had been disappointed, and, of course, what marks the child would bear? But I had only the satis|faction of perplexing, without convincing them.

The time of gestation is generally about nine months; but it is sometimes longer and some|times shorter. Many children are born in the seventh and eighth, and some not till after the ninth month: But, in general, the births before

the ninth month are more frequent than those that exceed that term.

It is generally believed, that children born in the eighth month cannot live, or, at least, that more of them die than of those who come into the world in the seventh month. This opinion appears to be paradoxical; and, if we consult experience, I believe it will be found to be er|roneous. A child born in the eighth month is more perfectly formed, and consequently more vigorous and lively, than one who is born in the seventh. This opinion, however, is very com|monly received, and is founded on the authori|ty of Aristotle: 'Caeteris animantibus ferendi uteri unum est tempus, homini vero plura sunt; quippe et septimo mense et decimo nascitur, atque etiam inter septimum et decimum positis; qui enim mense octavo nascuntur, etsi minus, tamen vivere possunt* 1.73.' The beginning of the seventh month is the earliest term of delivery. If the foetus be rejected sooner, it dies, and is denominated an abortion. Thus the time of gestation is more various in the human species than in other animals; for it extends from the 7th to the 10th, and, perhaps, to the eleventh month.

We are assured by women who have had ma|ny children, that females remain longer in the womb than males. If this be true, it is not sur|prising that female children should sometimes be

born in the 10th month. When infants come into the world before the 9th month, they are neither so large nor so well formed as those who appear not till a later period. Those, on the contrary, who remain in the womb till the 10th month, are larger and better made; their hair is longer; the growth of the teeth, though still concealed within the gums, is more advanced; and the tone of their voice is deeper and more distinct.

With regard to the occasional causes of deli|very, there is much uncertainty. It is imagined by some writers, that, when the foetus has ac|quired a certain size, the capacity of the uterus becomes too small for its retention, and that the restraint felt by the child obliges it to exert every effort to break its prison. Others alledge, which amounts nearly to the same thing, that the foe|tus becomes too heavy to be supported by the uterus, which, therefore, opens to be discharged of its load. Neither of these reasons appear to be satisfactory: The uterus has always sufficient capacity and strength to contain and support the weight of a child of nine months; for it is often loaded with two, during the same period; and it is certain, that the weight and size of two chil|dren of eight months, for example, exceed those of a single infant of the same age. Besides, it is not unfrequent that a child of nine months is less than another at eight months, though it still remains in the womb.

Galen pretends that the foetus continues in the uterus till it is able to take nourishment by the mouth, and that the want of proper food makes it restless, and anxious to escape. It has been said by others, that the foetus is originally nourished by the mouth, but that, in process of time, the liquor amnii is so contaminated with the urine and transpiration of the foetus, that it becomes perfectly disgustful, and obliges the child to use every method to effect its escape from the womb.

These reasons seem not to be more satisfactory than the former; for from them it would fol|low, that the smallest and weakest foetuses would necessarily remain longer in the womb than those of larger and more robust bodies; which is by no means the case. Besides, it is not for nourishment that the child, immediately after birth, seems to be anxious; for it can dispense with the want of it for a considerable time after: It appears, on the contrary, to be extremely de|sirous of easing itself of the superfluous load of nourishment (the meconium) received in the womb. This circumstance induced Drelincourt, and some other anatomists, to think, that the acrimony and uneasiness, arising from an ac|cumulation of excrement in the bowels, is the reason why they become restless, and use every effort to escape from the womb. I am not, I acknowledge, more satisfied with this explication

than the others. If the child is pressed with faeces, why does it not evacuate them in the liquor amnii? But this never happens. It ap|pears, on thè contrary, that the necessity of eva|cuating the meconium is not felt till after birth, when the motion of the diaphragm, occasioned by respiration, compresses the intestines, and gives rise to this evacuation; especially since no meconium was found in the amnios of a foetus of ten months, who had not respired, and since an infant of six or seven months discharges the meconium soon after respiration.

Other anatomists, and particularly Fabricius ab Aquapendente, imagined that the foetus left the uterus, from a desire of being refreshed by respiration. But this cause seems to be as chi|merical as any that has been mentioned. It is impossible that a foetus can have any idea of respiration; and far less can it have any concep|tion whether respiration would be agreeable or disagreeable.

After considering all these hypotheses, I su|spect that the delivery of the foetus depends on a cause of a very different nature. The men|strual flux returns at stated intervals. Though its appearance be interrupted by impregnation, its cause is not destroyed; and, though no blood is exhibited at the accustomed period; yet a re|volution in the system, similar to what happens before impregnation, must take place. It is for

this reason, that, in some women, the menses are not entirely suppressed during the first two or three months after conception. I imagine, therefore, that this periodic revolution happens as regularly after a woman has conceived as be|fore; but that the blood is prevented from flowing, by the excretories of the uterus being swelled and shut up, unless when it arrives in such large quantities, and acts with such force, as to overcome the resistance which is opposed to it. In this case, a great quantity of blood rushes out, and an abortion is the consequence. But it frequently happens, that a small quantity of blood appears, without producing this effect; because the blood has only been able to open a few of the canals or excretories of the uterus, while the rest remain entirely obstructed.

Though no blood appears, which is generally the case, the first revolution fails not to be ac|companied with the same painful symptoms. During the first suppression of the menses, therefore, the uterus is affected with a conside|rable agitation, which, when a little augmented, entirely destroys the product of generation. Hence, we may reasonably conclude, that few of those conceptions, which happen a short time before the accustomed return of the menses, are successful; because the action of the menstrual blood easily destroys the feeble roots of a germ so tender and so delicate. Those conceptions, on the contrary, which take place immediately

after this periodic discharge, succeed much bet|ter; because the foetus is allowed more time to grow, and to fortify itself against the action of the blood, when the next revolution happens in the system.

After the foetus has been enabled to resist the action of the first revolution, the increase of its growth, and of its attachment to the uterus, ren|der it still more capable of resisting any of the subsequent revolutions: Abortions, indeed, sometimes happen during every revolution; but they are more rare in the middle period of ge|station, than either at the beginning or near the end of it. Why they are more frequent at the beginning, has already been explained: It only remains to show why they are likewise more frequent towards the end.

The foetus generally comes into the world du|ring the tenth revolution of the menses. When it is born at the ninth or eighth, it lives, and is not, therefore, regarded as an abortion. Some have pretended to have seen instances of chil|dren born at the seventh, and even at the sixth revolution, who, notwithstanding this unfavour|able circumstance, continued to live. There is no difference between abortion and birth, but what relates to the living powers of the child. In general, the number of abortions in the first, second, and third months, for the reasons already assigned, is very great; and the number of pre|•••••…•••••… births, in the seventh and eighth months,

is also very great, in proportion to the abortions in the fourth, fifth, and sixth months; because, during this middle term of gestation, the pro|duct of generation having acquired strength and solidity sufficient to resist the action of the first four periodic revolutions, a more violent effort than any of the former is necessary to destroy it. For the same reason, an abortion is more difficult during the fifth and sixth months. But the foetus, which till now was weak, and could only exert its own force in a feeble manner, begins to move with more vigour; and, when the eighth revolution takes place, the efforts of the foetus uniting with those of the uterus, and facilitating its exclusion, the foetus may come into the world in the seventh month, and be in a capacity of living, whenever it happens to be unusually strong at this period. But, if the foe|tus be excluded solely from a weakness of the uterus, which renders it unable to resist the ac|tion of the blood during the eighth revolution, the birth of it is considered as an abortion, and the child dies. But such cases are uncommon; for, it the foetus has resisted the first seven re|volutions, nothing but particular accidents can prevent it from resisting the eighth, unless it has acquired more vigour than is common at this pe|riod. A foetus which has acquired the same degree of strength, but at a later period, will be excluded at the ninth revolution; and those which require nine months in obtaining this degree of

strength, will be born at the tenth revolution, which is the most usual term. But, when the foetus acquires not this degree of strength and perfection in nine months, it will remain in the uterus till the eleventh, or even the twelfth re|volution, that is, till the tenth or eleventh month: Of such late births many examples are record|ed.

Other reasons, to confirm the opinion, that the menstrual flux is the occasional cause of births at different periods, may be produced. The females of all animals which have no men|ses, bring forth very nearly at the same terms: The difference in the times of gestation is ex|tremely small. We may, therefore, conclude, that this variation, which is very great in wo|men, proceeds from the action of the menstrual blood, which is exerted at every periodic revo|lution.

We have already remarked, that the placenta adheres to the uterus only by the papillae; that there is no blood either in these papillae, or in the lacunae in which they are inserted; and that, when they are separated, an operation which requires no great effort, a milky liquor only is|sues from them. Why, therefore, is the birth of a child uniformly followed by a considerable haemorrhage, first of pure blood, and afterwards of blood mixed with a watery fluid? This blood proceeds not from the separation of the placen|ta; for the papillae are drawn out of the lacunae

without any effusion of blood. Delivery, there|fore, which is nothing more than this separa|tion, ought to produce no haemorrhage. Is it not more natural, on the contrary, to think, that the action of the blood is the cause of the birth; and that it is this menstrual blood alone which forces the vessels of the empty uterus, and be|gins to flow immediately after delivery, in the same manner as it did before conception?

We know, that, for some time after conception, the sack which contains the product of gene|ration, adheres not to the uterus. We have seen, from the experiments of De Graaf, that, by blowing upon the small globule, it is made to change its position. The adhesion to the uterus is never very strong: In the early periods of gestation, the placenta is slightly applied to the uterus; and those parts are only contiguous, or joined by a mucilaginous matter which has hard|ly any adhesion. How, then, should it happen, that, in abortions of the first or second month, this globule never escapes without being attend|ed with a great effusion of blood? This effusion cannot be occasioned by the passage of the glo|bule, which has no adhesion to the uterus. It is by the action of the blood, on the contrary, that the globule is extruded. Should we not, therefore, conclude, that this is the menstrual blood, which, by forcing the canals through which it was accustomed to flow before impreg|nation,

destroys the product of conception, and resumes its ordinary course?

The pains of child-bearing are principally occasioned by this action of the blood; for, it is well known, that they are equally violent in abortions of two or three months, as in ordinary births; and that many women feel, without ha|ving conceived, very acute pains, whenever the menstrual flux is about to appear. These pains are of the same kind with those which accompany abortions or births. Ought we not, therefore, to ascribe them to the same cause?

It appears, then, that the periodic revolution of the menstrual blood has great influence in child-bearing, and that it is the cause why the terms of delivery in women are more various than in other animals which are not subject to this discharge, and which always bring forth at the same times. It is also apparent, that the revolution occasioned by the action of the men|strual blood is not the only cause of birth: The action of the foetus itself contributes greatly to this end; for there are instances of children ha|ving made their escape from the uterus after the death of the mother, which could only happen from an exertion peculiar to the foetus.

The terms of gestation in cows, sheep, and other animals, are always the same, and no hae|morrhage attends their delivery. May we not, therefore, conclude, that the blood discharged by women after delivery is the menstrual

blood, and that the action of this blood upon the uterus, during every periodic revolution, is the reason why the human foetus is excluded at so many different terms? It is natural to i|magine, that, if the females of viviparous ani|mals had menses like women, their deliveries would be followed by an effusion of blood, and be equally various in their terms. The foetuses of animals are brought forth covered with their membranes; and it is seldom that the mem|branes are broken, or the waters flow before their delivery. But the birth of a child, with its membranes entire, is a rare phaenomenon. This circumstance seems to evince, that human foetuses make greater efforts to escape from their prison than those of other animals, or that the uterus of a woman affords not so free a pas|sage to the child; for it is by the struggles of the foetus against the resistance it meets with at the orifice of the uterus, that the membranes are torn.

RECAPITULATION.

ALL animals are nourished by vegetables, or by other animals which feed upon vege|tables. There is, therefore, in nature, a mat|ter common to both, which serves for the growth and nourishment of every thing that lives or vegetates. This matter can have no other mode of effecting growth and nourish|ment, but by assimilating itself to every part of the animal or vegetable, and by intimately pe|netrating the texture and form of these parts, which I have distinguished by the appellation of an internal mould. When this nutritive mat|ter abounds more than is sufficient for the growth and expansion of the animal or vege|table, it is detached from all parts of the body, and deposited in one or several reservoirs, under the form of a fluid. This fluid contains all the particles which are analogous to the different parts of the body, and, of course, all that is necessary for the reproduction of a being in miniature perfectly similar to the first. In most animals, this superfluity of nutritive matter does not take place till they have nearly acquired their full growth; and hence it is that animals are not capable of generating before this period.

When this nutritive and prolific matter, which is universally diffused, has passed through the internal mould of an animal or vegetable, and has found a proper matrix, it produces an ani|mal or vegetable of the same species. But, when it finds not a suitable matrix, it produces organized beings different from animals or ve|getables, as the moving and vegetating bodies which appear in the seminal fluids of animals, and in the infusions of the buds of plants, &c.

This prolific matter is composed of organic particles, which are always active, whose motions and actions are fixed or arrested by the brute parts of matter in general, and particularly by oily and saline substances; but, as soon as they are disengaged from this matter, which is fo|reign to their nature, they resume their action, and produce different species of plants, and other animated beings.

The effects of this prolific matter may be seen by the microscope in the seminal fluids of both male and female animals. The semen of vivi|parous females is siltrated through the glandu|lar bodies which grow upon their testicles; and these glandular bodies contain a considerable quantity of seminal fluid in their cavities. Ovi|parous females, as well as the viviparous, have a seminal fluid, which is still more active than that of the viviparous. The semen of the fe|male is, in general, similar to that of the male, when both are in a natural state. They decom|pose

in the same manner; they contain similar organic particles; and they exhibit the very same appearances.

All animal and vegetable substances contain a great quantity of this organic and prolific mat|ter. To discover it, we have only to sepa|rate it from the brute matter in which it is entangled; and this operation is effected by infusing animal or vegetable substances in water: The salts melt; the oils separate; and the or|ganic particles become evident by their move|ments. They abound more in the seminal fluid than in any other parts of animals; or rather, they are there more disengaged from the brute matter. Soon after flesh is infused, and while it is only slightly dissolved, the organic matter appears under the form of moving bodies, which are nearly as large as those in the seminal fluid. But, in proportion to the increase of the dissolu|tion, the size of the organic particles is diminish|ed, and their motion is augmented; and, when the flesh is entirely decomposed or corrupted, the organic particles are extremely minute, and their motion is inconceivably rapid. It is then that this matter may be poisonous, like that of the viper's tooth, in which Mr Mead perceived an infinite number of small pointed bodies, and which he imagined to be salts, though they are nothing but these same organic particles in an extremely active state. The pus which pro|ceeds from wounds may acquire such a degree

of putrescency, as to become a poison of the most active kind; for, whenever this active matter is exalted to a certain point, which may always be distinguished by the rapidity and mi|nuteness of the moving bodies it contains, it must become a species of poison. The same thing may be remarked with regard to the poi|son of vegetables. The same matter which nourishes us while in a natural state, will de|stroy us when it is corrupted, as appears from the gangrenes which affect the limbs of men and other animals, when they are fed with corrupt|ed grain; and from comparing the residue of the food which adheres to our teeth, with that which proceeds from the teeth of the viper or of a mad dog, which is nothing but the same matter too much exalted, and in the highest state of putrefaction.

When large quantities of this organic and prolific matter are collected in some part of an animal, where it is obliged to remain, it there forms living beings, which we have always re|garded as real animals. The taenia, the asca|rides, all the worms found in the veins, in the liver, in wounds, in pus, and most of those which are formed in putrified flesh, have no other ori|gin. The eels in paste, in vinegar, and all the pretended microscopic animals, are only diffe|rent forms assumed, according to circumstances, by this active matter, which has a perpetual tendency to organization.

In infusions of all animal and vegetable sub|stances, this prolific matter first discovers itself under the form of vegetation: We see it form into filaments, which grow and expand like plants; then their extremities and joints swell and burst, to give passage to a multitude of mo|ving bodies which have the semblance of animals. Nature, it would appear, begins all her opera|tions by a kind of vegetable motion: This mo|tion we perceive in a variety of microscopic ob|jects, and in the expansion of the animal embryo; for a foetus, at first, possesses only a species of vegetable growth or motion.

Sound food furnishes none of these moving particles for a considerable time: Fresh meat, grain, fruits, &c. require some days infusion before they exhibit any moving bodies. But the more any matter is corrupted, decomposed, or exalted, as pus, blighted grain, honey, the se|minal fluids, &c. these moving bodies the sooner make their appearance. In seminal fluids, they are entirely free from other matter; and only a few hours infusion are necessary to discover them in pus, corrupted grain, honey, strong drugs, &c.

The existence, therefore, of an organic ani|mated matter, universally diffused through all animal and vegetable substances, and which e|qually serves for their nourishment, their growth, and their reproduction, is apparent. Nutrition is effected by the intimate penetration of this

matter through every part of animal or vege|table bodies; expansion, or growth, is only a more extensive species of nutrition, which pro|ceeds as long as the parts are ductile, and ca|pable of being stretched; and reproduction is an effect of the same matter, when it superabounds in the body of an animal or vegetable. Every part of organized bodies sends off to proper re|servoirs the organic particles which are super|fluous for its nourishment: These particles are perfectly similar to the different parts from which they are detached, because they were destined for the nourishment of those parts. Hence, when the whole particles sent off from every part of the body are assembled, they must necessarily form a small body similar to the ori|ginal, because every particle is similar to the part from which it was detached. It is in this manner that every species of reproduction, where only one individual is requisite, as that of trees, plants, polypi, vine-fretters, &c. is ef|fected. This is also the first method employed by nature for the reproduction of such animals as require the aid of different sexes; for the se|minal fluid of each sex contains all the particles necessary for reproduction: But, to compleat the operation, something more is requisite, namely, the mixture of both fluids in a place suited to the expansion and growth of the foe|rus; and this place is the uterus of the female.

There are, therefore, no pre-existing germs, or germs infinitely contained within each other. But there is an organic matter diffused through all animated nature, which is always active, always tending to form, to assimilate, and to produce beings similar to those which receive it. The spe|cies of animals and of vegetables, therefore, can never be exhausted: As long as individuals subsist, the different species will be constantly new; they are the same now that they were three thousand years ago: The whole will per|petually exist by their own powers, unless they be annihilated by the will of their Creator.

Notes

• * 1.1

  This word is frequently used by the author, and requires to be explained. It signifies the power of producing or propa|gating in general, and is equally applicable to plants and to animals. Generation is a species of reproduction peculiar to animated beings.
• * 1.2

  This is not strictly true; for oysters, and even gall-insects, are capable of a degree of progressive motion.
• * 1.3

  The intelligent reader will perceive that this sentence, though not very obvious, contains the principle upon which the subsequent theory of generation adopted by the author is founded. It means no more than that the bodies of animals and of vegetables are composed of an infinite number of or|ganic particles, perfectly similar, both in figure and substance, to the whole animal or plant, of which they are the constituent parts.
• * 1.4

  Hae tam parvae quam magnae figurae (salium) ex magno solum numero minorum particularum, quae eandem figuram habent, sunt conflatae, sicuti mihi saepe licuit observare, cum aquam marinam aut communem in qua sal commune liquatum erat, 〈◊〉〈◊〉 or per microscopium, quod ex ea prodeunt elegantes, parvae, ac quadrangulares figurae adeo exiguae, ut mille earum myriades magnitudinem arenae crass••••ris ne aequent. Quae salis minutae particulae, quam primum oculis conspicio, magnitudine ab omnibus lateribus crescunt, suam tamen elegantem superficiem quadrangularem retinentes, fere . . . . . Figurae hae salinae cavitate donatae sunt, &c. See Leeuwenhoek, Arc. Nat. tom. I. p. 3.
• * 1.5

  To avoid the introduction of terms which might not be ge|nerally understood, it is necessary to inform the reader, that the phrases corbs organiques vivans, parties organiques vivantes, et mole|cules organiques vivantes, which occur so often in this volume, and form the basis of our auth r's theory, are uniformly, in the ver|sion, expressed by the words organic particles.
• * 1.6

  See this fully demonstrated in my preface to the French translation of Newton's fluxions, p. 7.
• * 1.7

  Here the Author gives an unnecessary recapitulation of Chap. III. to which the reader is referred.
• * 1.8

  See below the Nat. Hist. of Man, chap. 2.
• * 1.9

  Quod intra se semen jacit, foemina vocatur; quod in hac ••acit, mas; Aristot. de animalibus, art. 18.
• * 1.10

  See Needh. new microscopical discoveries, London 1745.
• * 1.11

  The translator thinks it his duty to apprize the reader, that here, as well as in several other parts of this work, the author makes an ingenious and plausible attack against the existence and utility of final causes. Every philosopher will admit the absurdity of employing a final cause as a physical principle. M. de Buffon, if he meant only to expose the misapplication of final causes, had no occasion to betray so much warmth and anxiety about an object so apparent. But, like too many of our modern French writers, he seems to be ignorant of, or rather intentionally neglects, the distinction between final and physical causes. Final causes regard the design or the utility of particu|lar objects, whether that utility relates to man, to the objects themselves, or to the general structure of the universe. But physical causes are limited to the explanation of particular ef|fects, or modes of existence. Why were mountains, seas, or in|sects, created? What useful purposes do they serve? For the so|lution of these, and similar questions, final causes can alone be employed. But if it be asked, How were mountains and seas formed? How were insects originally produced; and how are their different species propagated? These are questions purely physical, and so different in their nature from the former, that nothing but stupidity, or worse motives, could possibly confound them.

  It may be farther remarked, that final causes are the greatest stumbling-blocks which lie in the way of atheists and materialists. They, accordingly, strain every nerve to remove them. But their force is so irresistible; their numbers are so immense; their beauties are so striking, and correspond so intimately with the warm and benevolent feelings of the heart; the concatenation and mutual dependence of all created beings recognisable by our senses are so apparent, and so illustrious, that no powers of sophistry, no artful misrepresentations, no strokes of ridicule, will ever be able to diminish their influence, or weaken the force of those sentiments which the Supreme Being intended they should excite in the breasts of his intelligent creatures. Final causes not only demonstrate the existence of a Supreme Intelli|gent Power, but the infinite beneficence, and minute attention of that Power to the happiness of those beings upon whom He has thought proper to confer existence.
• * 1.12

  See Aristot. de Gen. lib. 1. cap. 20. and lib. 2. cap. 4.
• * 1.13

  See Deslandes dans son traité de la marine. Paris 1747.
• * 1.14

  See Hippocrat. lib. de Genitura, p. 129, et lib. de Diacta. p. 198. Lugd. Bat. tom. 1. 1665.
• * 1.15

  See Fefius's translation, tom. 1. p. 129.
• * 1.16

  See his Ornithologia.
• * 1.17

  Most of these facts are taken from Aristotle.
• * 1.18

  Two fleshy processes, one of which issues from each side of the fundus uteri, in the form of little horns, and are remarkable in some quadrupeds.
• * 1.19

  Hist. Anim. lib. 6. cap. ••.
• * 1.20

  See Langly observ. editae a Justo Schradero, Amst. 1674.
• * 1.21

  Malpighii pullus in ovo.
• * 1.22

  See Regn. Graaf, p. 242.
• * 1.23

  See Obs. Justi Schraderi, Amst. 1674.
• * 1.24

  Tom. 2. chap. 3. edit. De Bruxelles, 1710.
• * 1.25

  Hist. de l'acad. 1701.
• * 1.26

  See Verrheyen sup. anat. tom. 2. p. 69.
• * 1.27

  See nouvelles de la republic des lettres, ann. 1699, p. 552.
• * 1.28

  P. 1088, 〈◊〉〈◊〉 Ficini.
• * 1.29

  See opere del. Cav. Valisnieri, tom. 2. p. 105.
• * 1.30

  Année 1701, p. 111.
• * 1.31

  Published in the year 1745.
• * 1.32

  Here M. de Buffon mentions the advantages of the double microscope, and some precautions necessary in the management of it, which, now that the instrument is well known, and much improved since the author wrote, it is unnecessary to translate.
• * 1.33

  Needham's New Discoveries made with the Microscope, ch. 6. p. 53.
• * 1.34

  See Leeuwenh. Arc. nat. p. 306. 309. and 319.
• * 1.35

  See phil. trans. No. 141. p. 1041.
• * 1.36

  See phil. trans. No 141. p. 1043.
• * 1.37

  Here the author attempts a formal proof that Leeuwen|hoek invented the single microscope, and the existence of sper|matic animals, before Hartsoeker, which interrupts the argu|ment, is noways interesting to the reader, and is here omitted in the translation.
• * 1.38

  Tom. 〈…〉〈…〉
• * 1.39

  Tom. 1. p. 7.
• * 1.40

  Tom. 3. p. 92. 93.
• * 1.41

  See tom. 1. p. 163. and tom. 3. p. 101. of his works.
• * 1.42

  See tom. 4. p. 280. 281.
• * 1.43

  Tom. 4. p. 28.
• * 1.44

  See tom. 4. p. 304.
• * 1.45

  Tom. 1. p. 51.
• * 1.46

  P. 52.
• * 1.47

  P. 5.
• * 1.48

  Pag. 67.
• * 1.49

  See tom. 1. p. 160.
• * 1.50

  Tom. 2. p. 150.
• * 1.51

  Tom. 3. p. 93.
• * 1.52

  Tom. 3. p. 98.
• * 1.53

  Tom. 1. p. 26.
• * 1.54

  See tom. ••. p. 499. et tom. 3. p. 271.
• * 1.55

  See tom. 3. p. 370.
• * 1.56

  Tom. 3. p. 306.
• * 1.57

  See Harvey, Exercit. 64. and 65.
• * 1.58

  See Conrad. Peyer. Merycolog.
• * 1.59

  See Verheyen, sup. anat. tra. 5. cap. 3.
• * 1.60

  See Ruysch Thes. anat. p. 90. tab. VI. fig. 1.
• * 1.61

  Tom. 2. p. ••••••
• * 1.62

  See Leeuwenhoek, tom. 4. p. 91.
• * 1.63

  Mem. de l'Acad, année 1727, p. 32.
• * 1.64

  See chap. VI.
• * 1.65

  See Chap. ••••
• * 1.66

  See mem. de I'acad. des sciences, tom. 2. p. ••••.
• * 1.67

  P. 244.
• * 1.68

  January 1683.
• * 1.69

  Page 298.
• * 1.70

  See Comm. Acad. Petropol. vol. iv. pag. 261. and 262.
• * 1.71

  Harvey de Generat. p. 257.
• * 1.72

  See Vegetable Statics, chap. 6.
• * 1.73

  Vide de Generat. anim. l. 4. c. ult.