THE NEW EVOLUTION 



their active life in the wet or summer season and pass 

 the dry or winter season in a resting stage, commonly 

 the pupa, buried in the ground or in some other situa- 

 tion where they will not lose their moisture. 



Temperature is commonly regarded as an important 

 factor in controlling life both on the land and in the 

 sea. And so it is. Yet it seems to be not so impor- 

 tant of itself as in its indirect relation to organic life. 

 On land, changes in temperature, seasonal or diurnal 

 or irregular, profoundly affect every living thing. 

 This is due in part to their effect on the chemical 

 processes taking place within the body, but prob- 

 ably in equal part to the complexities they create 

 in the vital problem of securing and conserving 

 water. 



So far as plants and animals are concerned, one of 

 the most important things concerning water is that 

 at low temperatures it suddenly changes over into 

 ice — that is, it passes over into a form in which it 

 cannot be used without a considerable expenditure 

 of energy. 



So in the northern winter when the ground and 

 ponds and streams are frozen the plants cease to 

 grow and become dormant. The turtles, snakes, 

 lizards and frogs, the butterflies, bees, ants and other 

 insects, and the snails and earthworms, all pass into 

 the long sleep known as hibernation. All birds are 

 perpetually active, and all that cannot find sufficient 

 food fly south. But some mammals, like the bears 

 and woodchucks and certain of the mice, sleep like 

 the insects, while others, like the squirrels, sleep most 



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