Temperatures of Reptiles, etc 



59 



warm-blooded condition by sometimes developing a capacity for 

 heat-production in the action of their viscera. Dumeril has 

 shown that snakes by mere digestion can warm themselves from 

 2° to 4°, the maximum temperature occurring about twenty-four 

 hours after a meal. Moulting may warm a snake nearly a 

 degree, and frogs, lizards and serpents all warm up with amatory 

 emotion. 



Thus it constantly happens that these animals, though essen- 

 tially cold-blooded, may be observed at temperatures somewhat 

 above that of their environment. But in general that excess is 

 not great, and it leaves the distinction between the warm-blooded 

 and the cold-blooded type quite unaffected. 



The true criterion of the difference is of course the concomi- 

 tance of the temperature of the animal and its medium. An 

 animal of the warm-blooded type may vary a trifle in its general 

 body temperature when the climate alters, but it maintains an 

 almost constant degree of heat. The reptile, though it may 

 maintain itself a few degrees above the surrounding temperature, 

 always varies with it, rising and falling so as to keep always the 

 same number of degrees in excess. 



In two experiments I conducted to see how far this concomi- 

 tancy held, I placed two specimens of the large lizard already 

 mentioned into a small tank of water, so that only their noses 

 were above water. I then warmed up the water at various rates 

 of speed by means of one or more lamps. The following tables 

 will show how closely the lizards followed the temperature of the 

 enclosing water : — 



Lizards, Average Weight, 3o0 G-rams. 



