802 BIOLOGY. [Boor iv. 



from being the case. The same religious aad metaphysical pre- 

 judices which have been so deeply disquieted by the doctrine of 

 organic evolution are still more alarmed and annoyed by the 

 idea of spontaneous generation of any kind. It is only step by 

 step that those antiquated theories yield the ground to scientific 

 demonstra,tions. First of all it was denied that organised matter 

 had in itself the faculty of living. The equilibrium was only 

 maintained, it was thought, iu every organised being through the 

 perpetual intervention of an entity, of an archeus, of a vital 

 principle, of a soul, and so on, guiding and governing the vital 

 phenomena as a charioteer conducts a chariot, to use the expres- 

 sion of TertuUian. It becomes, however, unavoidable to admit 

 that there is no metaphysical dualism in the plant and in the 

 animal, but that they both live because they both combine in 

 themselves the conditions necessary and sufficient for an inces- 

 sant nutritive renovation. The doctrine of evolution has had 

 the same destiny. Not many years ago all naturalists, or almost 

 all, believed in the perfect immutability of the organised species, 

 and, as every epoch had its special fauna and flora, it was neces- 

 sary to recognise, with Cuvier, as in effect was done, a series of 

 successive creations, of visible or organic changes. "When God, 

 irreverently compared to the machinist of an opera, whistled 

 once, an implacable cataclysm annihilated all the living world ; 

 when he whistled a second time, but creatively, a new fauna and a 

 new flora rose to life. Thus had things to go on at every geo- 

 logical epoch. From the tribolite to the mammoth every species 

 had thus to be formed by magical crystallisation. Assuredly 

 there was here a spontaneous generation of the most astonishing 

 kind, but it shocked no one, because it was in more or less tacit 

 accordance with metaphysical and' religious ideas. But little by 

 little the idea of miracle has been driven from this domain as 

 from so many others. It became inevitable to confess that the 

 geological epochs had not been separated by abysses, that the 

 cataclysms, where there had been any, had only been partial ; 

 that the modifications and transformations of the soil had been 



