But it is right here to examine the ideas of Aristotle more generally on the subject of generation, because this great philosopher has written the most on the subject, and treated it the most generally. He distinguishes animals into three classes; first, those which have blood, and, excepting some few, multiply by copulation; the second, those which have no blood, but, being at the same time both male and female, produce of themselves, and without copulation; and thirdly, those bred by putrefaction, which do not owe their origin to parents of any kind. I shall first remark, that this division must not be admitted of; for though in fact all kinds of animals which have blood are composed of males and females, it is not equally true, that animals who have no blood are for the most part male and female in one; for we are only acquainted with the snail and worm on earth which are in this state; nor can we ascertain whether all shell-fish, and other animals which have no blood, be hermaphrodites. With respect to those animals which he says proceed from putrefaction, as he has not enumerated them, many exceptions occur; for most of the kinds which the ancients thought engendered by putrefaction have been discovered by the moderns to be the produce of eggs.
After this he makes a second division of animals; those which have the faculty of moving themselves progressively, as walking, flying, swimming, and those which have no such faculty. All animals which can move, and have blood, have sexes; but those which, like oysters, are adherent, or who scarcely move at all, have no sex, and are, in this respect like plants, distinguished only, as he says, into males and females by difference of size. It is not yet ascertained whether shell-fish have sexes or not; there are in the oyster-kind fruitful individuals, and others which are not so; those which are fruitful are distinguished by a delicate border which surrounds the body of the oyster, and they are called males.[BN]
[BN] See the observation of M. Deslandes, in the Tracte de la raine, Paris, 1747.
But to proceed, the male, according to Aristotle, includes the principle of generative, motion, and the female contains the material parts of generation. The organs which serve for this purpose are different in the different kind of animals; the principal are the testicles in the males, and the matrix in the females. Quadrupeds, birds, and cetaceous animals, have testicles; fish and serpents are deprived of them; but they have both proper conduits to receive and prepare the seed. These essential parts are always double, both in the male and female, and serve in males to stop the motion of the blood, which forms the seed. This he proves by the example of birds, whose testicles swell in the season of their amours, and diminish so greatly when this season is over that they are scarcely perceptible.
All quadrupeds, as horses, oxen, &c. which are clothed with hair, and cetaceous fishes, as dolphins and whales, are viviparous; but cartilaginous animals, and vipers, are not truly viviparous, because they produce an egg within themselves before the live animal appears. Oviparous animals 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 perfection after they have been laid in the water by the female; and in all kinds of oviparous animals, excepting birds, the females are generally larger than the males, as fishes, lizards, &c.
After having mentioned these general varieties in animals, Aristotle begins with examining the opinion of the ancient philosophers, that the seed, as well of the male as of the female, proceeded from all parts of the body; he declares against this opinion, because, he says, although children often resemble their fathers and mothers, they also sometimes resemble their grandfathers; and, besides, they resemble their parents by the voice, hair, nails, carriage, and manner of walking. Now the seed, he continues, cannot proceed from the hair, voice, nails, or any external quality, like that of walking; therefore children do not resemble their parents because the seed comes from every part of the body, but for some other reason. It appears to me unnecessary here to point out the weakness of these arguments; I shall only observe that it appears to me this great man expressly sought after methods to separate himself from the sentiments of those philosophers who preceded him; and I am persuaded, that whoever reads his treatise on generation with attention, will discover that a strong design of giving a new system, different from that of the ancients, obliged him always to give the preference to the least probable reasons, and to elude, as much as he could, the force of proofs, when they were contrary to his general principles of philosophy.
According to Aristotle the seminal liquor is secreted from the blood; and the menstrua, in females, is a similar secretion, and the only one which serves for the purpose of generation. Females, he says, have no other prolific liquor; there is, therefore, no mixture of that of the male with that of the female. He pretends to prove this from some women conceiving without receiving the least pleasure, and because few women emit this liquor externally during copulation; that in general those who are brown, and have a masculine appearance, do not emit at all, yet engender equally with those who are more fair in complexion and feminine in appearance, and whose emissions are considerable. Thus he concludes woman furnishes nothing but the menstrual. This blood is the matter of generation; and the seminal fluid of the male does not contribute as matter but as form; it is the efficient cause, the principle of motion; it is to generation what the sculptor is to a block of marble: the liquor of the male is the sculptor, the menstrual blood the marble, and the fœtus the image.
The menstrual blood receives from the male seed a kind of soul, which gives life and motion. This soul is neither material nor immaterial, because it can neither act upon matter nor enter in generation as matter, the menstrual blood being all that is necessary for that purpose. It is, says our philosopher, a spirit, whose substance is like that of the starry region. The heart is the first work of this soul; it contains in itself the principle of its own growth; and it has the power to arrange the other members. The menstrual blood contains every other principle of all the parts of the fœtus: the soul, or spirit, of the male seed, makes the heart begin to act, and that communicates the power of bringing the other viscera to action; and thus, successively, is every part of the animal unfolded and brought into motion. All this appeared very clear to our philosopher; there only remained to him one doubt, which was, whether the heart was realized before the blood; and in fact he had reason for this doubt; for, although he had adopted the opinion of the heart existing first, Harvey has since pretended, by reasons of the same kind as those used by Aristotle, that it was not the heart but the blood which is first realized.
This is the system that great philosopher has given us of generation, and I shall leave it to the opinion of the reader whether that of the ancients, which he rejects, can be more obscure or more absurd than his; nevertheless, his system has been followed by most of the learned. Harvey has not only adopted the ideas of Aristotle, but has added new ones of the same kind. As this system of generation is of the same kind as the rest of Aristotle's philosophy, where form and matter are the grand principles; where the vegetative and sensitive are the active beings in Nature; and where final causes are real objects; I am not surprised that it has been received by scholastic authors; but it is astonishing that so able a physician and observer of Nature as Harvey was, should be carried away with the stream, while every physician followed the opinion of Hippocrates and Galen; which we shall explain in order. We must not, however, imbibe a disadvantageous idea of Aristotle from the above exposition of his System of Generation. It would be like judging of Descartes by his Treatise on Man. The explanations which these two philosophers give of the formation of the fœtus should not be considered as complete systems on the subject of generation; they are rather general consequences drawn from their philosophical principles.
END OF THE SECOND VOLUME.