n8 The Science of Life. 



almost no ancient embryology. There are, indeed, re- 

 cords to the effect that more than two thousand years 

 Ancient Em- ago, in Greece, inquiring eyes bent over the 

 bryology. chick developing within the egg, as they do 

 still in our laboratories, but the methods of investiga- 

 tion were awanting, and the most elementary facts were 

 either unperceived or misunderstood. Moreover, it 

 must be remembered that the wide-spread belief in spon- 

 taneous generation, and the common habit of inventing 

 metaphysical explanations of vital processes, tended to 

 stifle embryological inquiry. 



The one great exception was Aristotle, whose genius 

 foresaw what Harvey more explicitly declared two 

 thousand years afterwards. Harvey quotes a sentence 

 from Aristotle which deserves to be remembered : ( ' All 

 living creatures, whether they swim, or walk, or fly, 

 and whether they come into the world with the form of 

 an animal or of an egg, are engendered in the same 

 way". And one of the most scholarly of embryologists, 

 Prof. Whitman, has said "that part of Harvey's theory 

 which affirms that the parts of the future organism do 

 not pre-exist as such, but make their appearance in due 

 order of succession, and which is so often cited as the 

 essence of epigenesis, was all clearly stated by Aris- 

 totle". 



After Aristotle, the first important name in the his- 

 tory of embryology is that of William Harvey (1578- 

 e immortal discoverer of the circu- 



Harve 



lation of the blood. Working "in the har- 



ness of Aristotle", he maintained that "all animals are 

 in some sort produced from eggs", but the aphorism 

 "omne vivum ex ovo", so persistently ascribed to him, 

 was not his, nor must it be supposed for a moment that 

 the word egg meant to Harvey what it means to us. 

 He maintained that practically every organism begins 

 its individual life from an apparently simple primordium 

 in which "no part of the future offspring exists de facto, 

 but all parts inhere in potentia" . But since he had no 

 conception of what we now call "genetic continuity" 

 which links the germ-cells of successive generations in 

 a continuous lineage, he was quite unable to suggest 



