No. 534] INFLUENCE OF CHANGED CONDITIONS 371 



dition for development is a certain amount of moisture, 

 for the insects die when subjected to higher tempera- 

 tures within dry vessels. The main effect of increase of 

 temperature seems to be to hasten the rate of develop- 

 ment. Probably it is the relative thickness of the 

 chorion of the eggs that proves their chief protection 

 under changed external conditions. 



The experiments on this moth and on Attacus would 

 show that the cocoon can have no particular value by ex- 

 eluding the sunlight, for we have found that sunlight is 

 not injurious to the eggs and pupa\ Probably the main 

 value of an insect cocoon is that of protecting against 

 enemies, though it may also be of service in preserving 

 a proper amount of moisture; for cocoons soak up the 

 rain and melting -now. and would retain it for a con- 

 siderable while. 



