animals, is confirmed and made manifest by all that passes in the egg, viz. : that all the parts are not formed at once and together, but in succession, one after another ; and that there first exists a particular genital particle, in virtue of which, as from a beginning, all the other parts proceed. As in the seeds of plants, in beans and acorns, to quote particular instances, we see the gemmula or apex, protruding, the commencement of the entire prospective herb or tree. " And this particle is like a child emancipated, placed independently, a principle ex- isting of itself, from whence the series of members is subse- quently thrown out, and to which belongs all that is to con- duce to the perfection of the future animal." l Since, there- fore, " No part engenders itself, but, after it is engendered, concurs in its own growth, it is indispensable that the part first arise which contains within itself the principle of increase ; for whether it be a plant or an animal, still has it within itself the power of vegetation or nutrition ;" 3 and at the same time distinguishes and fashions each particular part in its several order ; and hence, in this same primogenate particle, there is a primary vital principle inherent, which is the author and original of sense and motion, and every manifestation of life.
That, therefore, is the principal particle whence vital spirit and native heat accrue to all other parts, in which the calidum innatum sive implantatum of physicians first shows it- self, and the household deity or perennial fire is maintained; whence life proceeds to the body in general, and to each of its parts in particular; whence nourishment, growth, aid, and solace flow ; lastly, where life first begins in the being that is born, and last fails in that which dies.
All this is certainly true as regards the first engendered part, and appears manifestly in the formation of the chick from the egg. I am therefore of opinion that we are to reject the views of certain physicians, indifferent philosophers, who will have it that three principal and primogenate parts arise together, viz. : the brain, the heart, and the liver; neither can I agree with Aristotle himself, who maintains that the heart is the first engendered and animated part ; for I think that the privilege of priority belongs to the blood alone ; the blood being that
1 De Gen. Aniin. lib. ii, cap. i. 2 Ibid. cap. 4.
