Coral, corallum , It is the most beautiful and the most precious of all the substances that we improperly call marine plants. ( See Pl., XXII of Histoire naturelle , figure 3 . ) [1] One cannot address any of these productions without recalling the name and discovery of M. Peyssonel, the correspondent of the Royal Academy of Sciences who first found that these so-called plants belong to the animal kingdom—for they are produced by sea-insects. M. Peyssonel, being, in 1725, on the Barbary Coast, by order of the king, discovered that the so-called coral flowers observed by M. the Count of Marsigli were in fact insects, which he called coral nettles . Our observer extended the same discovery to several other species of the same kind, such as madrepores, lithophytes, sponges, etc. He has continued his research until the present, and he still pursues it to this day in Guadaloupe, where he resides in the capacity of medical botanist to the king. In the month of August, 1753, he sent to us, M. de Buffon and me, the copy of a work that he wrote on this matter, and which comprises the history of the so-called marine plants and his own observations on this subject. I would hasten to render an account here to the public, if I had the consent of M. Peyssonel to dispose in this manner of the deposit that he entrusted to us.

I may not better fulfill this function than by the observations that M. Donati has made on coral , and that he gave to the public in his book, titled Della storia naturale marina dell'adriatico saggio, etc., in Venice, 1750, in 4º [quarto]. The descriptions there are made in an easy style, such that it is more suitable to give them an exact translation than to report them back excerpted.

Coral , according to some, draws its name from the Greek words κόρειν, to adorn, and ἁλός, sea , as if there were no other marine production whose beauty could be compared to coral : and there is no aspect of it on which neither the ancients nor the moderns have written much.

The feelings of writers on the nature of coral have been divided. Some placed it among the number of stones; others believed that it was the product of a precipitation of earth-salts and other elements mixed together, as well as of contrasts between them; the largest number reported it within the vegetable kingdom; and finally, it found itself some naturalists who showed that it was a veritable zoophyte.

Coral is a sea plant that much resembles a branch of a small tree stripped of its leaves. It has no roots, but for a base it has a foot, whose form, without being constant, most often approaches a circle. This foot applies itself to all the points of the surface of the body on which it finds itself, much as one would make wax—firmly compressed; and it attaches itself so thoroughly, that it is impossible to separate. It serves as the base and support of the coral , but it does not contribute in any way to its nourishment, as branches have been found that have been separated from their foot for a long time, but they have continued to live, grow, and reproduce at the bottom of the sea. From this foot rises a stem for its own food, and whose larger end—in this, old corallers, that is to say, fishermen of coral , have assured me—scarcely passes the size of a Parisian inch. This stem does not ordinarily sprout more than a small number of branches, which branch out themselves. All its branches are nearly always separate; however, one sometimes sees two and even more of them that originate and rise in parallel, which are as if thrown together, and so united that it is impossible to perceive how they lie. It is more common to see those that, meeting, unite themselves in the same manner; and I observed more than one time a single branch that rose from two other branches thus united.

It is worthwhile to point out that if a mollusk fastens itself to the stem or branches of coral , without fail it becomes covered, in whole or in part, by the same substance of coral .

I have observed that its greatest height, to which it rises very rarely in the Adriatic Sea, is a Parisian foot, or a little more. The stem and the branches are usually round: nevertheless, rather often one finds some, and I preserve them in my collection, that are flat and broad.

The foot, the stem, and the branches are made of a uniform substance; and this substance consists of a bark and a fundamental material, which are the same in all these parts.

This fundamental material is the internal substance of coral , which comes close to the hardness of marble, even if it is at the bottom of the sea. At the ends of the branches it is less hard than the bark; it keeps its consistency in the area of these ends, and the greatest hardness is in the stem and the most considerable branches.

This substance, when viewed using a microscope in corals of a single color, such as red, and in those that have not been altered by insects, appears homogenous, pure, without stains, without cavities, of an equal grain, of a uniform hardness, and amenable to a finer polish. But such does not obtain in corals of several colors, not even sometimes in those of a yellowish-rose color, or in those truly colored rose. I have some branches of this species of coral , a transversal cut of which shows different concentric layers the color of yellowish-rose, white, and more or less saturated with color. One observes the same concentric layers in red coral that has been a little exposed to the action of fire; they are all light brown, but separated by other, much more dark layers.

However hard this substance is, when by time or chance it has lost its bark, it is prone to be gnawed upon by a small insect that worms its way into it through very small openings, and which destroys its internal structure. This structure consists of small, nearly round cells that connect among themselves, and which are separated by very slender walls. Coral eaten away in this manner is weak, fragile, and cannot be used for anything. There is another insect of the same kind that tunnels through the coral in a straight line, and whose route is marked by cylindrical holes. As for the rest, I must advert that the hardest marbles that find themselves on the bottom of the sea are not exempt from the attacks of these insects, or of other insects that resemble them perfectly.

The fundamental material of coral is grooved, according to its length; these grooves, which start from the foot, consistently maintain a parallelism among themselves and with the branches that they run across; they are more marked on the main stem and the large branches—sometimes they even disappear on the small ones; their surface is uneven and rough, as if they were formed from a great number of very small blood cells. The material in question, having been exposed to a violent fire, reduces to a very fine dust, of the same color as ordinary ash: and as with virgin ash, that is to say, that which has been taken from burning coal, one discovers under a microscope a sort of skeleton formed from fibers and vessels of a ligneous substance; thus, in the ash of the internal substance of coral , one also perceives, with the aid of a microscope, these constituent parts, which appear to to be of the same shape and of the same color as that of the ash of the bark: they are small, white corpuscles, nearly spherical, and they are close-knit, as in the form of grapes. Several times, in the transversal cut of coral branches that have been broken, I have seen grooves that go out from the center, and that end in an exact correspondence to the grooves of the surface.

All this surface is immediately surrounded by a pale, white cellular body, of a moderately soft consistency, formed by networks of small, vascular membranes that receive through capillary vessels a whitish sap that gives its color to the reticular body. To these membranes are attached some red blood cells, united together by other small membranes. These blood cells entirely resemble, in size and shape, those from the ash of the internal substance and bark of coral ; from which it follows that these bodies are inalterable to the point that calcination makes no difference other than to change their color.

The reticular body that immediately envelops the fundamental material of coral regularly deposits there its small red blood cells—these which form the spherical rough edges from which the surface of the grooves is formed. From this, one can conclude for certain that the material of coral is composed of these blood cells. If one asks me from where they derive their origin, I shall respond without hesitation that they derive it from coral polyps: for, if it is true, as one shall see below, that their eggs are wrapped in similar bodies, one must conclude that bodies of the precise same nature, wherever they find themselves, are the work of the same polyps.

From the reticular body extends a soft bark, of a color a little lighter than that of the internal substance; it is formed from very slender nets, to which are attached a great number of red blood cells that hold together, and that communicate their color to the bark. One discovers in it under a microscope vessels cylindrical and parallel among themselves, which from every side throw off branches into the small membranes of which I have spoken above, and which bring there the milky sap that feeds the coral .

The surface of this bark is uneven, slippery on coral newly fished; more raised up in certain places, in others more flat: in several one perceives by eye some kinds of knots that rise up above the surface; they are round, rather broad at their base, more narrow toward their upper surface, and they are divided into eight more or less equal sections, which come together at the center of each knot, or rather of each cell composed internally of a section of the reticular body and coated externally in coral bark.

In certain places, the reticular body forms a fold, or a kind of small sack that covers the whole interior of the cell, up to the upper edge; and so, the cell does not end immediately at the fundamental material of the coral , but at the reticular body. The shape of these cells is that of a cone that has a bulge whose diameter is greater than that of its base, and whose blunt top forms in the hard material of coral small cavities more marked in young and slender branches but less noticeable in larger and older branches.

The bottom of each cell looks upon the foot of the stem, and the mouth is turned to the opposite side; this is the home of the polyp, which one can see with the naked eye, but whose precise shape one cannot distinguish without the aid of a microscope. It is thus that I have observed it, in order to describe and draw it.

From each cell goes out and is deployed a white insect, soft, a little transparent, in the shape of a star with eight equal rays, nearly conical and lined in part with other, also conical appendages, which all have the same direction as the ray from which they originate. These rays are a little flat, and from their common center rises a shell that broadens toward its base, which has a rather large opening at its top, and which is furrowed along its length by eight deep grooves, whose spaces form eight prominent lines: it is in these spaces that each ray has its insertion-point. The shell has for support a sort of foot-stalk, which I should rather call the belly of the animal , which always stays in the cell, as long as the polyp is alive and does not suffer, although it does not cling there in any way, much as one can observe when the insect is in certain positions. All this is seen in coral recently fished and kept in seawater; for when one draws it from the water, or even touches it in the water, immediately the polyp returns to its cell and the shell snaps shut; and the rays, along with their appendages, withdraw themselves using a game similar to that of the horns of clams, retreat toward their origin, and arrange themselves on the edges of the shell. The polyp presents itself in the following form when it has just been withdrawn from its element; in this state, viewed without a microscope, it resembles a drop of milk; and the older fishermen commonly take it for coral milk, especially as, by pressing the bark, one can make it come out of the polyp in the manner of a milky sap; it is this that makes me believe that the milk that Andre Cesalpin first observed in coral was none other than the polyps that we now consider. The belly of these insects, as we have said, does not cling at all to its cell, but nevertheless it is useful to them in securing it, by contracting and expanding itself enough, so that its diameter surpasses that of the mouth of the cell. This game is seen very clearly when one separates the cell and the polyp from the hard material of the coral : not only does one perceive the belly in its state of contraction, but also the circumstance that brings the polyp into its cell.

I have noticed in the lower part of the belly of certain polyps very small, round bladders, extremely soft, transparent, pale or yellowish, which I have taken, given their shape and the place where they are found, for true polyp eggs.

Although the diameter of these eggs is perhaps no more than the fortieth part of a ligne, I believe that I have discovered in them some traces of the small blood cells that enter into the composition of the bark and entire substance of coral ; these eggs detach themselves from the animal, and by the softness of their consistency they attach themselves to the bodies on which they fall, then they expand toward their base, they inflate a little, and then one can clearly distinguish their cavity, whose upper edge becomes furrowed with eight grooves but does not open itself again. The embryo of the polyp takes shape and stays there for a certain time, then, having developed, and having become, as it were, an adult, it sorties out through an opening that occurs in the upper surface of the cell and blossoms outside, and from that proceeds the growth of coral . As long as this first cell or polyp egg is again shut, everything there is in a state of softness; but when it is open, one begins to notice there some small, hard blades; finally, when it has reached a ligne-and-a-half in diameter, it swells at the top and at the bottom, and contracts itself toward the middle of its height; it is then that it takes the true consistency of coral . In the measure that suits them, the polyps multiply and form new branches. Donati, page 43 and following . See Polyparia.

1. Probably Buffon’s Histoire Naturelle, générale et particulière, avec la description du Cabinet du Roi (1749–1804).