200 BIOLOGY AND ITS MAKERS 



the development of the chick. Except the figures of Coiter 

 (1573), those of Fabricius were the earliest published illus- 

 trations of the kind. Altogether his figures show develop- 

 mental stages of the cow, sheep, pig, galeus, serpent, rat, and 

 chick. 



Harvey's own treatise was not illustrated. With that 

 singular independence of mind for which he was conspicuous, 

 the vision of the pupil was not hampered by the authority of 

 his teacher, and, trusting only to his own sure observation 

 and reason, he described the stages of development as he 

 saw them in the egg, and placed his own construction on 

 the facts. 



One of the earliest activities to arrest his attention in the 

 chick was a pulsating point, the heart, and, from this observa- 

 tion, he supposed that the heart and the blood were the first 

 formations. He says: "But as soon as the egg, under the 

 influence of the gentle warmth of the incubating hen, or of 

 warmth derived from another source, begins to pullulate, 

 this spot forthwith dilates, and expands like the pupil of the 

 eye; and from thence, as the grand center of the egg, the 

 latent plastic force breaks forth and germinates. This first 

 commencement of the chick, however, so far as I am aware, 

 has not yet been observed by any one." 



It is to be understood, however, that the descriptive part 

 of his treatise is relatively brief (about 40 pages out of 350 in 

 Willis's translation), and that the bulk of the 106 " exercises " 

 into which his work is divided is devoted to comments on the 

 older writers and to discussions of the nature of the process 

 of development. 



The aphorism, " omne vivum ex ovo,^'' though not invented 

 by Harvey, was brought into general use through his writings. 

 As used in his day, however, it did not have its full modern 

 significance. With Harvey it meant simply that the embryos 

 of all animals, the viviparous as well as the oviparous, orig- 



