We, therefore, in conformity with the method proposed, shall show in the first place in the egg, and then in the conceptions of other animals, what parts are first, and what are subsequently formed by the great God of Nature with inimitable providence and intelligence, and most admirable order. Next we shall inquire into the primary matter out of which, and the efficient cause by which generation is accomplished, and also the order and economy of generation, as observed by us; that from thence, from its own work, we may have some certain information of the several faculties of the formative and vegetative soul, and of the nature of the soul itself, judging from its members or organs, and their functions.
This, indeed, cannot be done in all animals: first, because a sufficient number of several of these cannot be commanded; and again, because, from the small size of many, they escape our powers of vision. It must suffice, therefore, that this is done in some kinds which are more familiarly known to us, and that we refer all the rest to these as types or standards.
We have, therefore, selected those that may tend to render our experiments more undeniable, viz. the larger and more perfect animals, and that are easily within reach. For in the larger animals all things are more conspicuous; in the more perfect, they are also more distinct; and in those that we can command, and that live with us, everything is more readily examined: we have it in our power so often as we please to repeat our observations, and so to free them from all uncertainty and doubt. Now, among oviparous animals of this description, we have the common fowl, the goose, duck, pigeon; and then we have frogs, and serpents, and fishes; crustacea, testacea, and mollusca; among insects, bees, wasps, butterflies, and silkworms; among viviparous creatures, we have sheep, goats, dogs, cats, deer, and oxen; lastly, we have the most perfect of all animals, man.
Having studied and made ourselves familiar with these, we may turn to the consideration of the more abstruse nature of the vegetative soul, and feel ourselves in a condition to understand the method, order, and causes of generation in animals generally; for all animals resemble one or other of those above mentioned, and agree with them either generally or specifically, and are procreated in the same manner, or the mode of their generation at least is referrible by analogy to that of one or other of them. For Nature, perfect and divine, is ever in the same things harmonious with herself, and as her works either agree or differ, (viz. in genus, species, or some other proportion,) so is her agency in these (viz. generation or development) either the same or diverse. He who enters on this new and untrodden path, and out of the vast realm of Nature endeavours to find the truth by means of anatomical dissections and experiments, is met by such a multitude of facts, and these of so unusual an aspect, that he may find it more difficult to explain and describe to others the things he has seen, than he reckoned it labour to make his observations; so many things are encountered that require naming; such is the abundance of matter and the dearth of words. But if he would have recourse to metaphors, and by means of old and familiar terms would make known his ideas concerning the things he has newly discovered, the reader would have little chance of understanding him better than if they were riddles that were propounded; and of the thing itself, which he had never seen, he could have no conception. But then, to have recourse to new and unusual terms were less to bring a torch to lighten, than to darken things still more with a cloud: it were to attempt an explanation of a matter unknown by one still more unknown, and to impose a greater toil on the reader to understand the meaning of words than to comprehend the things themselves. And so it happens that Aristotle is believed by the inexperienced to be obscure in many places; and on this account, perhaps, Fabricius of Aquapendente rather intended to exhibit the chick in ovo in his figures than to explain its formation in words.