294 THE FITNESS OF THE ENVIRONMENT 



of those that are regularly passed on, that 

 accumulate and create new species. In gen- 

 eral, when species have begun to diverge from 

 a common stock, they accentuate their diver- 

 gence as they progress in their evolution. 

 Yet, in certain definite points, they may 

 evolve identically ; in fact, they must do so 

 if the hypothesis of a common impetus be 

 accepted. This is just what we shall have to 

 show now in a more precise way, by the same 

 example we have chosen, the formation of 

 the eye in molluscs and vetebrates. The idea 

 of an 'original impetus,' moreover, will thus 

 be made clearer." 1 . . . "If life realizes 

 a plan, it ought to manifest a greater harmony 

 the further it advances, just as the house 

 shows better and better the idea of the archi- 

 tect as stone is set upon stone. If, on the 

 contrary, the unity of life is to be found solely 

 in the impetus that pushes it along the road of 

 time, the harmony is not in front, but behind. 

 The unity is derived from a vis a tergo: it 

 is given at the start as an impulsion, not 

 placed at the end as an attraction. In com- 

 municating itself, the impetus splits up more 

 and more. Life, in proportion to its progress, 

 is scattered in manifestations which un- 



1 Bergson, "Creative Evolution," translated by Mitchell. 

 New York, 1911, pp. 87, 88. 



