CHAPTEK IV 



RESPONSES OF POIKILOTHERMS TO VARIATIONS IN 

 TEMPERATURE 



It has long been recognized that, in so far as body 

 temperature is concerned, animals may be divided into 

 two large groups. These have been referred to as the 

 cold-blooded and the warm-blooded animals. The first 

 group includes animals, poikilotherms, in which body 

 temperature changes with that of the environment; the 

 second group includes those animals, homoiotherms, 

 which maintain at all times a practically constant tem- 

 perature which is inherently independent of the environ- 

 ment. In this chapter the responses of poikilotherms to 

 heat and cold will be discussed. 



Body Temperature of the Poikilotherms. — The lower 

 vertebrates and all of the invertebrates belong in the 

 group of variable temperature animals. Only the birds 

 and mammals possess a means of regulating their body 

 temperature which makes them independent of the tem- 

 perature of the environment. How close the poikilo- 

 therms approximate the temperature of their environ- 

 ment cannot be stated with certainty. It mil be seen 

 from Table I that not all investigators agree. Many 

 of the conflicting results reported as to the tem- 

 perature of poikilotherms are likely due to the methods 

 employed. By the use of precision instruments many 

 of the variations may be eliminated and a better under- 

 standing of temperature relations now is being acquired. 



17 



