Anatomical exercitations concerning the generation of living creatures to which are added particular discourses of births and of conceptions, &c. / by William Harvey ...

That an Egg is the Common Original of all Animals. (Book 62)

EXER. LXII. (Book 62)

ANimals, saith Aristotle, have this in common to∣gether with Plants; that some do spring out of * 1.1 seed, and some of their own accord: for as Plants do either arise from the seed of other Plants, or else spring up of their own accord, having attained some princi∣ple fit for their production: and some of them do at∣tract aliment to themselves out of the earth, and some again are bred in other plants: so some Animals are generated by the cognation or affinity of their form; and some of their own accord, no seed at all proceeding which is of kin to them: whereof some are generated out of putrefied earth or plants, (as several Insects) o∣thers are begotten in Animals themselves, and out of the excrements of their parts. But this is common to all those (whether they be generated of their own accord, or else in other Animals, or out of the putrefaction of their parts, or their excrements) namely, to arise out of some principle fit for that purpose, and by some efficient contained in that principle: so that All living creatures must of ne∣cessity have a principle out of which, and by which they are begotten. Give me leave to call this principle, Primordium vegetale, the vegetal principle;

namely, some corporeal substance, having life in it in potentiâ, or something subsisting of it selfe, which is apt to be transformed into a vegetative form, by some internal principle acting in it: Name∣ly, such a principle as the Egge, and the seed of Plants is: such is the conception of Viviparous Ani∣mals, and the Worm of Insects, as Aristotle calls it: the principles of divers Animals being also diverse, according to the diversitie of which principles, the manner of the generation of Animals is diverse likewise: and yet they all consent and agree in this, that they spring from a vegetal principle, as out of a matter indowed with an efficient or pro∣ductive virtue; but differ, in that this principle doth either result casually, or of its own accord, or else proceed from something pre-existent, (as the fruit thereof.) Whereupon those Animals are called sponte nascentia, spontaneous productions, these à parentibus genita, ofsprings derived from their parents. They are also distinguished from their manner of Birth; for some of them are Ovi∣parous, others Viviparous: to which Aristotle ad∣deth * 1.2 Vermiparous. But if we may distinguish them, as they fall under sense, there are onely two Spe∣cies or sorts of productions; namely, these: all A∣nimals do either produce an Animal Actu, actual∣ly; or potentiâ, potentially. Those Animals which produce an Animal actu, are called Viviparous; and those that produce an Animal in potentiâ, Ovipa∣rous. For every principle which is only alive in po∣tentiâ, we (with Fabricius) do conceive, ought to be called Ovum, an Egge: and as for that principle which Aristotle calls Vermis, a Worm, we do not at all distinguish it ab Ovo, from an Egg; and that because it looks like one to the eye, and also be∣cause that indistinction seems consonant to rea∣son.

For that Vegetal Principle, which is alive in potentiâ, is also an Animal in potentiâ. Nor is that distinction which Aristotle puts between an Egge, and a Worm, to be allowed of; for he calls that an Egge, ex cujus parte fit Animal, out of part of which an Animal is made: quod autem totum mu∣tatur, * 1.3 nec ex parte ejus Animal gignitur, est Vermis: and that a Worm, which is wholly transformed, and doth not produce an Animal out of some part of it only. But now these two do both agree in this, that they are productions not yet alive, but Animals onely in potentiâ; and therefore are both Eggs.

And Aristotle himself calls the very same things * 1.4 Worms in one place, and Eggs in another: And treating of Locusts, saith, There eggs are corrupted in Autumn, when it is wet weather: and (speaking of Grashoppers) When the litle worm, saith he, grow∣eth in the ground, it becomes Tettigometra, a Grass∣hopper-matrix: and a litle after, The females taste the sweeter after coition; for they have white egges. Nay, in that very place, where he had raised a di∣stinction between a Worm and an Egge, hee adds; * 1.5 But all this kinde of litle worms, when it hath attained the end of its magnitude, is made a kinde of Egge; for their shell doth harden, and so long they continue with∣out motion: which is apparent in the worms of Bees, and Wasps, and also in the Canker-worm. And in∣deed every body may see, that the first rudiments of Spiders, Silkworms, and other Insects, are to be no less ranked in the classis and scale of Eggs, then the spawn, or Egges of Fishes which have softer shells, or of Fishes which have no shells at all, and almost of all sort of fishes whatsoever: which Spawn of theirs is not actually an animate body, but yet Animals are begotten out of them. Since

therefore those creatures which do produce actu Animal, a Creature actually alive, are called Vi∣viparous: doubtless, those Animals which do bring forth a creature which is alive in potentiâ, must be called Oviparous Animals, or else they cannot be comprehended under any Common notion; especi∣ally, seeing such Productions are vegetal Rudi∣ments, proportionable to the seeds of Plants, such as an egge also is allowed to be. We must therefore conclude, that all Animals are either Viviparous, or Oviparous.

But because there are several species of Oviparous Animals, therefore the difference of Eggs is also several. For any kinde of Rudiment is not a com∣petent Recipient of every kinde of animal form. Though therefore Eggs in a large or general ac∣ceptation do not differ, yet since some are perfect, and some imperfect, they are justly distinguished. Perfect Eggs we call those, which are perfected in the Uterus, and obtain there a requisite magni∣tude, before they are layed: as the Eggs of Fowle. But those we call Imperfect, which are excluded ere they are ripe, and have not yet attained their just bulk, but do expect that abroad, after they are layed; as the Spawn or Eggs of Fishes, that have a softer shell, and of Fishes which have none at all; and likewise the Rudiments of Insects (which Ari∣stotle calls Worms) are to be listed in this rank: as also the Rudiments of those Creatures which are spontaneous productions.

Moreover, though some kindes of perfect Egges are party-coloured, as being compounded of a yolk and white; yet some of them are only of one single colour, as constituted of a white alone: so also amongst imperfect Eggs, others are properly so called, as out of which a perfect Animal is pro∣duced,

as out of the Egges of Fishes: and others improperly, from whence an imperfect Animal proceeds; namely, a Worm, or Canker-worm; which is a kinde of Medium between a perfect, and an imperfect Egge: which in respect or compari∣son of its own egge, or Rudiment from whence it sprung, is an Animal indowed with Sense and Mo∣tion, and doth nourish it self; but in comparison of a Flye, or Butterflie, whose rudiment is in po∣tentiâ, it is to be counted no better then a crawling-egge, sustaining it selfe: like to a Canker-worm, which having now attained its perfect magni∣tude, is transformed into an Aurelia, or perfect Egge; and now ceasing to move any longer, like a very Egge indeed, is an Animal in potentiâ.

In like manner, though there are some Eggs, out of whose whole and entire substance (by a Meta∣morphosis, or Transformation) a perfect Animal is formed, which is not fed by any remaining por∣tion of the Egge, but instantly seeks out for its maintenance abroad: and other Eggs, out of part of which a Foetus is constituted, and nourish∣ed by the remainder; though (I say) there are so many several sorts and diversities of Eggs, yet nothing stands in the way, to forbid those to be called Eggs, which Aristotle stiles Worms, (if we may give judgement upon things, according as they discover themselves to our sense and reason) since they are all Vegetal principles, not actually Animals, but in potentiâ, & the true seeds of Animals, proportionable to the seeds of Plants; as we have long since demonstrated in a Hen-egg. All Ani∣mals therefore, are Viviparous, or Oviparous; be∣cause they either produce an Animal actually a∣live, or else an Egge, or Rudiment, which is an Animal, not actu, but in potentiâ.

The Generation therefore of all Oviparous Ani∣mals may be reduced to the example of Hen-eggs, or at least be easily deduced from thence: because the same things which are related in their history, may be discovered in the rest of Viviparous crea∣tures.

But hereafter, when we treat of the Generation of Insects, and of Spontaneous productions, we shall discover how each of them are either differenced amongst themselves, or do else agree. For since every generation is a path-way to the attaining of the form of every Animal: according as Animals are either like, or unlike one another, so that their parts do neither specifically, nor generical∣ly agree; so likewise is it usuall in their Genera∣tions. For Nature, who is a Perfect Operatrix, and consonant to her self in her Operations, doth de∣sign Parts that are alike, to Operations and Fun∣ctions that are alike and agree; and so likewise to the attainment of the same form, and the same end, she treads the same steps, and persists alwaies in the same method in the Generation of Animals.

Hereupon, in every perfect party-coloured egge of any fowle whatever (which is compounded of a Yolk and White, and fenced with a Shell) as we have still observed the same parts, as are in a Hen-egg, so have we ever found the same order and method of generating, and constituting the foetus (as in a Hen-egg.) And the self same things may also be observed in the Eggs of Serpents, and all Oviparous four-footed Animals, as the Tortoise, Froggs, and Li∣zards; as from whose perfect and party-coloured egges, the foetus is framed and produced, the same way, as in others of the like kinde. But how Spi∣ders, and the softer Shell-fish, as Lobsters, and Shrimps, and the race of Fishes that have scales and

no shells, as the Cuttle-fish and the Calamire do get out of their Eggs, or Spawn; as also how Worms, and Catterpillars do first creep out of the Eggs of Insects, out of which, at length retreating into the worm or vermine called Aurelia, (as into other new eggs again) at last a common Flie, or Butter∣flie is generated; how these Creatures, I say, doe differ in their Generation out of Eggs, from the brood arising out of Hen-eggs, shall be declared in its due place.

Lastly, though all party-coloured egges are not generated and fructified the same way; but some become prolifical by the Coition of a Male and Fe∣male, and others by other meanes, as the egges or frie of Fishes; and though there be also a differ∣ence in the manner of the growth of Egges, inso∣much as some are nourished and encreased within their parents bowels, and others abroad: yet no∣thing hinders, why a foetus may not be produced out of any egge whatsoever, (in case it be a perfect egge) as well as out of a Hen-egge. Wherefore, the History wherein we have already unfolded the ge∣neration of a Hen-egge, is satisfactory and full e∣nough for the knowledge of the Generation of all other Oviparous creatures beside; as likewise to the knowledge of all those things which doe thence ensue, by way of Corollary, or Dedu∣ction.

Notes

• * 1.1

  Hist. an. l. 1. c. 1.
• * 1.2

  Hist. an. l. 1. c. 5.
• * 1.3

  Gen. an. l. 3. c. 7. Hist. an. l. 1. c. 5.
• * 1.4

  Hist. an. l. 5. c. 29. Ibid. c. 30.
• * 1.5

  Gen. an. l. 3. c. 9.