24 



HOMOIOTHERMISM 



therefore, that poikilotherms may have a higher body 

 temperature than that of their immediate environment 

 through the absorption of radiant energy. In a very 

 warm environment highly pigmented animals commonly 

 find long exposures to sunlight deleterious, and seek the 

 shade or are nocturnal. In a colder environment pig- 

 mentation may be of considerable value because it would 



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TIME IN MINUTES 



Fifl. 2. — ^Rise in body temperature of a turtle when placed three feet 

 away from a radiant source of energy. The circumjacent tempera- 

 ture remained unchanged. 



aid in the absorption of heat. The temperature of a 

 body is a determining factor in the amount of radiation 

 from it. The total heat-loss by radiation is proportional 

 to the difference between the fourth powers of the abso- 

 lute temperatures of the body and its environment, if 

 the area and nature of the surface remain constant. It 

 follows then that a poikilotherm would lose little heat 



