198 EVOLUTION IN BIOLOGY vi 



precursor and model, with the generous respect with 

 which one genuine worker should regard another 

 that such germs may arise by a process of 

 " equivocal generation " out of not-living matter ; 

 and the aphorism so commonly ascribed to him, 

 " omne vivum ex ovo" and which is indeed a fair 

 summary of his reiterated assertions, though 

 incessantly employed against the modern advo- 

 cates of spontaneous generation, can be honestly 

 so used only by those who have never read a 

 score of pages of the " Exercitationes." Harvey, 

 in fact, believed as implicitly as Aristotle did in the 

 equivocal generation of the lower animals. But, 

 while the course of modern investigation has only 

 brought out ioto greater prominence the accuracy 

 of Harvey's conception of the nature and mode of 

 development of germs, it has as distinctly tended 

 to disprove the occurrence of equivocal generation, 

 or abiogenesis, in the present course of nature. 

 In the immense majority of both plants and 

 animals, it is certain that the germ is not merely 

 a body in which life is dormant or potential, but 

 that it is itself simply a detached portion of 

 the substance of a pre-existing living body ; and 

 the evidence has yet to be adduced which will 

 satisfy any cautious reasoner that " omne vivum 

 ex vivo" is not as well-established a law of 

 the existing course of nature as " omne vivum 

 ex ovo." 



In all instances which have yet been investi- 



