The student of development finds, not only that the chick commences its existence as an egg, primarily identical, in all essential respects, with that of the Dog, but that the yelk of this egg undergoes division—that the primitive groove arises, and that the contiguous parts of the germ are fashioned, by precisely similar methods into a young chick, which, at one stage of its existence, is so like the nascent Dog, that ordinary inspection would hardly distinguish the two. The history of the development of any other vertebrate animal, Lizard, Snake, Frog, or Fish, tells the same story.

Ch.2, p. 79. - Evidence as to Man's Place in Nature (1863)