The yelk, although only a minute speck in the ovary, gaining by degrees in depth of colour and increasing in size, gradually acquires the dimensions and characters that distinguish it at last. Cast loose from the cluster, it descends by the infundibulum, and, transmitted through the spirals and cells of the processus uteri, it becomes surrounded with albumen; and this, without in any place adhering to the uterus (as was rightly observed by Fabricius in opposition to Aristotle), or growing by means of any system of umbilical vessels; but as the eggs of fishes and frogs, when extruded and laid in the water provide and surround themselves with albumen, or as beans, vetches, and other seeds and grains swell when moistened, and thence supply nourishment to the germs that spring from them, so, from the folds of the uterus that have been described, as from an udder, or uterine placenta, an albuminous fluid exudes, which the vitellus, in virtue of its inherent vegetative heat and faculty, attracts and digests into the surrounding white. There is, indeed, an abundance of fluid having the taste of albumen, contained in the cavity of the uterus and entangled between the folds that cover its interior. In this way does the yelk, descending by degrees, become surrounded with albumen, until at last, having in the extreme part of the uterus acquired a covering of firmer membranes and a harder shell, it is perfected and rendered fit for extrusion. EXERCISE THE TENTH. _Of the increase and nutrition of the egg._ Let us hear Fabricius on these topics. He says: “As the action of the stomach is to prepare the chyle, and that of the testes to secrete the seminal fluid, (because in the stomach chyle is discovered, and in the testes semen,) so we declare the act of the uterus in birds to be the production of eggs, because eggs are found there. But this, as it appears, is not the only action of uteri; to it must be added the increase of the egg, which succeeds immediately upon its production, and which proceeds until it is perfected and attains its due size. For a fowl does not naturally lay an egg until it is perfect and has attained to its proper dimensions. The office of the uterus is, therefore, the growth as well as the generation of the egg; but growth implies and includes the idea of nutrition; and, as all generation is the act of two principles, one the agent, another the matter, the agent in the production of eggs is nothing else than the organs or instruments indicated, viz., the compound uterus; and the matter nothing but the blood.”