Page:The Works of William Harvey (part 1 of 2).djvu/372

 in the same way as the seeds of plants are justly entitled their eggs, not only as being the matter or that from which, but the efficient or that by which the pullet is engendered. In which finally no part of the future offspring exists de facto, but in which all parts inhere in potentia.

The seed, properly so called, differs however from the geni- ture, which by Aristotle is defined to be ' ' that which, proceeding from the generator, is the cause, that which first obtains the principle of generation; in those, to wit, whom nature destined to copulate. But the seed is that which proceeds from these two in their connection : and such is the seed of all vegetables, and of some animals, in which the sexes are not distinct; like that which is first produced by male and female commingled, a kind of promiscuous conception, or animal; for this already possesses what is required of both."

The egg consequently is a natural body endowed with animal virtues, viz. principles of motion and rest, of transmutation and conservation ; it is, moreover, a body which, under favorable circumstances, has the capacity to pass into an animal form ; heavy bodies indeed do not sink more naturally, nor light ones float, when they are unimpeded, than do seeds and eggs in virtue of their inherent capacity become changed into vegetables and animals. So that the seed and the egg are alike the fruit and final result of the things of which they are the beginning and efficient cause.

For a single pullet there is a single egg; and so Aristotle 1 says : " from one seed one body is engendered ; for example, from a single grain of wheat one plant ; from a single egg one animal; for a twin-egg is, in fact, two eggs."

And Fabricius 2 with truth observes : " The egg is not only an exposed uterus, and place of generation, but that also on which the whole reproduction of the pullet depends, and which the egg achieves as agent, as matter, as instrument, as seat, and all else, if more there be, that is needful to generation." He shows it to be an organ because it consists of several parts, and this, from the statement of Galen, who will have the very es- sence of an organ to be that " it consist of several parts, all of

1 Gen. Anim. lib. i, cap. 20. 2 Loc. cit. p. 47.