338 THE BIOLOGY OF THE SEASONS 



of the fires of life so that there is extremely slow com- 

 bustion, and it works well as long as the external tempera- 

 ture does not fall below +1 C. It is probably also very 

 useful in giving the organs and tissues of the body a long 

 rest a rest even from eating. It represents an interesting 

 reminiscence of a more primitive physiological state when 

 the temperature-regulating mechanism was not yet well 

 established in the ancestral mammals. Of this primitive 

 condition we have a permanent illustration in the Mono- 

 tremes, which are imperfectly warm-blooded. Thus the 

 temperature of the Spiny Ant-eater (Echidna) varies with 

 that of its surroundings through the extraordinary range 

 of 10 C. a fine instance of a physiological connecting 

 link between cold-blooded and warm-blooded. And that 

 is just what every hibernating mammal also illustrates. 



