362 



Comparative Animal Physiology 



TABLE 61. NORMAL BODY TEMPERATURES AND LETHAL 

 TEMPERATURES OF HOMOIOTHERMIC ANIMALS 



dogs and men when the testes are intra-abdominal or are heated in the scrotum. 

 There are exceptions, however, as in the monotremes and insectivores, the 

 whale, elephant, rhinoceros and seal, all of which have intra-abdominal testes. 

 In birds the testes are intra-abdominal; however, spermatogenesis is said to 

 occur only at night, when body temperature declines, and in some birds the 

 testes migrate into a space between air sacs during the breeding season. 



The more primitive mammals have lower body temperatures during normal 

 activity than do higher mammals, and their temperature, although well above 

 that of the environment, fluctuates with air temperature. The poorly regula- 

 ting lower mammals are heterothermic (Table 62). Temperature regulation 



