FUNCTION AND ENVIRONMENT 197 



the parent provokes a variation in the off- 

 spring. The best instances, as yet, are to be 

 found in the experiments carried on for many 

 years by Tower on beetles of the genus 

 Leptinotarsa, which he subjected to unusual 

 conditions of temperature and humidity, when 

 the male and female reproductive organs of 

 the parent were at a certain stage in their 

 development. The body of the parent ex- 

 hibited 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 mark- 

 ings, and even in minute details of structure. 

 And there was no reversion to the parental 

 condition. 



(7) Another " organism-environment " rela- 

 tion 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 difficulties. The physical 

 world is careless of life; one living creature 

 presses upon another, competes with another, 

 devours another. Thus, while the environ- 

 ment is a stimulus, it is also a sieve. It has 

 an eliminating action which, as we have seen, 

 is often discriminate; it sifts and winnows; 

 the result is extinction for some, but adapta- 



