I however am of opinion that the uses of the chalazæ are no other than those I have assigned them, namely, that they serve as poles to the microcosm of the egg, and are the association of all the membranes convoluted and twisted together, by which not only are the several fluids kept in their places, but also in their distinct relative positions. But I have absolute assurance that the spot or cicatricula in question is of the very highest importance; it is the part in which the calor insitus nestles; where the first spark of the vital principle is kindled; for the sake of which, in a word, the whole of the rest of the fluids and all the membranes of the egg are contrived. But this has been already insisted on above.
Formerly, indeed, I did think with Fabricius that this cicatricula was the remains or trace of the detached peduncle; but I afterwards learned by more accurate observation that this was not the case; that the peduncle, by which the vitellus hangs, was infixed in no such limited space as we find it in apples and plums, and in such a way as would have given rise to a scar on its separation. This peduncle, in short, expands like a tube from the ovary on towards the vitellus, the horizon of which it embraces in a bipartite semicircle, not otherwise than the tunica conjunctiva embraces the eye; and this in suchwise that the superior part of the vitellus, or the hemisphere which regards the ovary, is almost free from any contact or cohesion with the peduncle, in the superior part of the cup or hollow of which nevertheless, but somewhat to the side, the spot or cicatricula in question is placed. The peduncles becoming detached from the vitelli can therefore in no way be said to leave any trace of their attachments behind them. Of the great importance of this spot in generation I have already spoken in the historical portion of my work.
But I have still, always following my old teacher Fabricius as my guide on the way, to treat of the uses of the cavity in the blunt end of the egg.
Fabricius enumerates various conveniences arising from this cavity, according to its dimensions. I shall be brief on the subject: it contains air, and is therefore useful in the ventilation of the egg, assisting the perspiration, refrigeration, and respiration, and finally the chirping of the chick. Whence this cavity, small at first, is larger by and by, and at last becomes of great size, as the several offices mentioned come into play.
Thus far have we spoken of the generation of the egg and chick, and of the uses of the several parts of the egg; and to the type exhibited we have referred the mode of generation of oviparous animals in general. We have still to speak of the generation of viviparous animals, in doing which we shall as before refer all to a single familiarly known species.
EXERCISE THE SIXTY-SECOND.
An egg is the common origin of all animals.
“Animals,” says Aristotle,[323] “have this in common with vegetables, that some of them arise from seed, others arise spontaneously; for as plants either proceed from the seed of other plants, or spring up spontaneously, having met with some primary condition fit for their evolution, some of them deriving their nourishment from the ground, others arising from and living on other plants; so are some animals engendered from cognate forms, and others arise spontaneously, no kind of cognate seed having preceded their birth; and whilst some of them are generated from the earth, or putrefying vegetable matter, like so many insects, others are produced in animals themselves and from the excrementitious matters of their parts.” Now the whole of these, whether they arise spontaneously, or from others, or in others, or from the parts or excrements of these, have this in common, that they are engendered from some principle adequate to this effect, and from an efficient cause inherent in the same principle. In this way, therefore, the primordium from which and by which they arise is inherent in every animal. Let us entitle this the primordium vegetale or vegetative incipience, understanding by this a certain corporeal something having life in potentia; or a certain something existing per se, which is capable of changing into a vegetative form under the agency of an internal principle. Such primordia are the eggs of animals and the seeds of plants; such also are the conceptions of viviparous animals, and the worm, as Aristotle calls it, whence insects proceed: the primordia of different living things consequently differ from one another; and according to their diversities are the modes of generation of animals, which nevertheless all agree in this one respect, that they proceed from the vegetal primordium as from matter endowed with the virtue of an efficient cause, though they differ in respect of the primordium which either bursts forth, as it were, spontaneously and by chance, or shows itself as fruit or seed from something else preceding it. Whence some animals are spoken of as spontaneously produced, others as engendered by parents. And these last are again distinguished by their mode of birth, for some are oviparous, others viviparous, to which Aristotle[324] adds a vermiparous class. But if we take the thing as simple sense proclaims it, there are only two kinds of birth, inasmuch as all animals engender others either in actu—virtually, or in potentia—potentially. Animals which bring forth in fact and virtually are called viviparous, those that bring forth potentially are oviparous. For every primordium that lives potentially, we, with Fabricius, think ought to be called an egg, and we make no distinction between the worm of Aristotle and an egg, both because to the eye there is no difference, and because the identity is in conformity with reason. For the vegetal primordium which lives potentially is also an animal potentially. Nor can the distinction which Aristotle[325] made between the egg and the worm be admitted: for he defines an egg to be that “from part of which an animal is produced; whilst that,” he says elsewhere,[326] “which is totally changed, and which does not produce an animal from a part only, is a worm.” These bodies, however, agree in this, that they are both inanimate births, and only animals potentially; both consequently are eggs.
And then Aristotle himself, whilst he speaks of worms in one place, designates them by the name of eggs in another.[327] Treating of the locust, he says,[328] “its eggs become spoiled in autumn when the season is wet;” and again, speaking of the grasshopper, he has these words, “when the little worm has grown in the earth it becomes a matrix of grasshoppers (tettigometra);” and immediately afterwards, “the females are sweeter after coitus, for then they are full of white eggs.”
In this very place, indeed, where he distinguishes between an egg and a worm, he adds:[329] “but the whole of this tribe of worms, when they have come to their full size, are changed in some sort into eggs; for their shell or covering hardens, and they become motionless for a season, a circumstance that is plainly to be seen in the vermiculi of bees and wasps, and also in caterpillars.” Every one indeed may observe that the primordia of spiders, silkworms, and the like, are not less to be accounted eggs than those of the crustacea and mollusca, and almost all fishes, which are not actually animals, but are potentially possessed of the faculty of producing them. Since, then, those creatures that produce actually are called viviparous, and those that produce potentially either pass without any general distinguishing title or are called oviparous and particularly as such productions are vegetal primordia, analogous to the seeds of plants, which true eggs must needs be held to be, the conclusion is, that all animals are either viviparous or oviparous.