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 vivuwm 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 into 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- 
