title="[8]"/> of his times but one single principle, which is, that heat and cold produce spirits, and that those spirits have the power of ordering and arranging matter. He has viewed generation more like a physician than a philosopher, while Aristotle has explained it more like a metaphysician than a naturalist; which makes the defects of Hippocrates's system particular and less apparent, while those of Aristotle's are general and evident.

These two great men have each had their followers; almost all the scholastic philosophers, by adopting Aristotle's philosophy, received his system of generation, while almost every physician followed the opinion of Hippocrates; and seventeen or eighteen centuries passed without any thing new being said on the subject. At last, at the restoration of literature, some anatomists turned their eyes on generation, and Fabricius Aquapendente was the first who made experiments and observations on the impregnation and growth of the eggs of a fowl. The following is the substance of his observations.

He distinguished two parts in the matrix of a hen, the one superior and the other inferior. The superior he calls the Ovarium, which is properly no other than a cluster of small yellow eggs of a round form, varying in size from the bigness of a mustard-seed to that of a large nut or medlar. These small eggs are fastened together by one common pellicle, and form a body which nearly resembles a bunch of grapes. The smallest of these eggs are white, and they take another colour in proportion as they increase.

Having examined these eggs immediately after the communication of the cock, he did not perceive any remarkable difference, nor any of the male semen in any one of these eggs; he therefore supposed that every egg, and the ovarium itself, became fruitful by a subtle spirit, which came from the semen of the male; and he says, that in order to secure this fecundating spirit, nature has placed at the external orifice of the vagina of birds a kind of net-work or membrane, which permits, like a valve, the entrance of this seminal spirit, but at the same time prevents it from re-issuing or evaporating.

When the egg is loosened from the common pellicle, it descends by degrees through a winding passage into the internal part of the matrix. This passage is filled with a liquor nearly similar to the white of an egg; it is also in this part that the eggs begin to be surrounded with this white liquor, with the membrane which occasions it, the two ligaments (chalazæ) which passes over the white, and connects it with the yolk and shell, which are formed in a very short time before they are laid. These ligaments, according to Fabricius, is the part of the egg fecundated by the seminal spirit of the male; and it is here where the fœtus first begins to form. The egg is not only the true matrix, that is to say, the place of the formation of the chick, but it is from the egg all generation depends. The egg produces it as the agent: it supplies both the matter and the organs; the ligaments are the substance of formation; the white and the yolk are the nutriment, and the seminal spirit of the male is the efficient cause. This spirit communicates to the ligaments at first an alterative faculty, afterwards a formative, and lastly the power of augmentation, &c.

These observations of Fabricius have not given us a very clear explication of generation. Nearly at the same time as this anatomist was employed in these researches, towards the middle of the sixteenth century, the famous Aldrovandus[C] also made observations on eggs; but as Harvey judiciously observes, he followed Aristotle much closer than experiment. The descriptions he gives of the chicken in the egg are not exact. Volcher Coiter, one of his scholars, succeeded much better in his enquiries; and Parisanus, a physician of Venice, having also laboured on this subject, they have each given a description of the chicken in the egg, which Harvey prefers to any other.

This famous anatomist, to whom we are indebted for the discovery of the circulation of the blood, has composed a very extensive treatise on generation; he lived towards the middle of the last century, and was physician to Charles I. of England. As he was obliged to follow this unfortunate prince in his misfortunes, he lost what he had written on the generation of insects among other papers, and he composed what he has left us on the generation of birds and quadrupeds from his memory. I shall concisely relate his observations, his experiments, and his system.

Harvey asserts that man and every animal proceed from an egg; that the first produce of conception in viviparous animals is a kind of an egg, and that the only difference between viviparous and oviparous is, that the fœtus of the first take their origin, acquire their growth, and arrive at their entire expansion in the matrix; whereas the fœtus of oviparous animals begins to exist in the body of the mother, where they are merely as eggs, and it is only after they have quitted the body of the mother that they really become fœtuses; and we must remark, says he, that in oviparous animals, some hold their eggs within themselves till they are perfect, as birds, serpents and oviparous quadrupeds; others lay their eggs before they are perfect, as fish, crustaceous, and testaceous animals. The eggs which these animals deposit are only the rudiments of real eggs, they afterwards acquire bulk and membranes, and attract nourishment from the matter which surrounds them. It is the same, adds he, with insects, for example, and caterpillars, which only seem imperfect eggs, which seek their nutriment, and at the end of a certain time arrive to the state of chrysalis, which is a perfect egg. There is another difference in oviparous animals: for fowls and other birds have eggs of different sizes, whereas fish, frogs, &c. lay them before they are perfect, have them all of the same size; he indeed observes, that in pigeons, who only lay two eggs, all the small eggs which remain in the ovarium are of the same size, and it is only the foremost two which are bigger than the rest. It is the same, he says, in cartilaginous fish, as in the thornback, who have only two eggs which increase and come to maturity, while those which remain in the ovarium are, like those in fowls, of different sizes.

He afterwards makes us an anatomical exposition of the parts necessary to generation, and observes, that in all birds the situation of the anus and vulra are contrary to the situation of those parts in other animals; the anus being placed before and the vulra behind;[D] and with respect to the cock, and all small birds, that they generate by external friction, having in fact no intermission nor real copulation; with male ducks, geese, and ostriches, it is evidently otherwise.

Hens produce eggs without the cock, but in a very small number,