FUNCTION AND ENVIRONMENT 197 



in their development. The body of the 

 parent exhibited no modification, but the 

 external influence, saturating through the 

 body, was sometimes operative on the germ- 

 cells and thus on the offspring. In some 

 cases there were remarkable changes in 

 colour and markings, and even in minute 

 details of structure. And there was no 

 reversion to the parental condition. 



(7) Another "organism-environment" re- 

 lation is that implied in the struggle for 

 existence, which in its widest and truest 

 sense includes all the reactions of living 

 creatures to their surroundings and diffi- 

 culties. The physical world is careless of 

 life; one living creature presses upon an- 

 other, competes with another, devours an- 

 other. Thus, while the environment is a 

 stimulus, it is also a sieve. It has an eliminat- 

 ing action which, as we have seen, is often 

 discriminate; it sifts and winnows; the 

 result is extinction for some, but adaptation, 

 and this it may be a degree more perfect, 

 for others. 



(8) But we must not think of the matter 

 too fatalistically, as if organisms were always 

 like helpless fishes, around which the environ- 

 mental net closed, only the little ones getting 

 through the meshes. True, they cannot by 

 taking thought increase or decrease their 



