with the reciprocal interchange of generation and decay; and as the sun, now in the east and then in the west, completes the measure of time by his ceaseless revolutions, so are the fleeting things of mortal existence made eternal through incessant change, and kinds and species are perpetuated though indivi- duals die.
The writers who have treated of this subject have almost all taken different paths; but having their minds preoccupied, they have hitherto gone to work to frame conclusions in consonance with the particular views they had adopted.
Aristotle, 1 among the ancients, and Hieron. Fabricius of Aquapendente, among the moderns, have written with so much accuracy on the generation and formation of the chick from the egg that little seems left for others to do. Ulyssus Aldro- vandus, 2 nevertheless, described the formation of the chick in ovo; but he appears rather to have gone by the guidance of Aris- totle than to have relied on his own experience. For Volcherus Goiter, living at this time in Bologna, and encouraged, as he tells us, by Aldrovandus, his master, opened incubated eggs every day, and illustrated many points besides those noted by Aldrovandus ; 3 these discoveries, however, could scarcely have remained unknown to Aldrovandus. TEmilius Parisanus, a Venetian physician, having discarded the opinions of others, has also given a new account of the formation of the chick from the egg.
But since our observations lead us to conclude that many things of great consequence are very different from what they have hitherto been held to be, I shall myself give an account of what goes on in the egg from day to day, and what parts are there transmuted, directing my attention to the first days espe- cially, when all is most obscure and confused, and difficult of observation, and in reference to which writers have more par- ticularly drawn the sword against one another in defence of their several discordant observations, which, in sooth, they accommodate rather to their preconceived opinions respecting the material and efficient cause of animal generation than to simple truth.
What Aristotle says on the subject of the reproduction of
1 Hist. Anim. lib. vi, cap. 2, 3. * Ornithol. lib. xiv.
3 Nobil. Exercit. lib. vi.
