ii HABIT? AND NATURAL HISTORY OF THE FROG 55 



lower amphibia is very marked. Triton is able to regen- 

 erate its tail or limbs, or even its eye, if a small portion 

 of that organ is left. But in the frog, and, so far as is 

 known, in the other Anura, the power of regeneration is 

 almost entirely lost. Even in the tadpole stage it is much 

 reduced. The tadpoles of the higher amphibia are able to 

 regenerate the tail if it is cut off, but their power of regen- 

 erating the limbs is very limited. The regeneration of the 

 limbs of tadpoles was first recorded by Spallanzani. Fraisse, 

 however, who cut off the limbs from both young and old 

 tadpoles, arrived at entirely negative results. Later Barfurth 

 carried on several experiments on both old and young tad- 

 poles, and found that if the legs were cut off from young 

 specimens these organs would be frequently regenerated, 

 although slowly. The power of the tadpole to regenerate 

 missing limbs was found to decrease rapidly with age. 



Effects of Heat and Cold. — The frog belongs among 

 those animals which are commonly spoken of as cold- 

 blooded. This expression doubtless takes its origin from 

 the fact that the temperature of such forms is usually low. 

 The higher vertebrates, such as the mammals and birds, 

 have a high bodily temperature, and, what is most remarka- 

 ble, the temperature in most of these keeps nearly constant 

 under most diverse conditions. A bird or a mammal may 

 live in extremes of climate below 40 and 50 below zero 

 F. and considerably over ioo° F., and yet the tem- 

 perature of the blood will not vary more than a small 

 fraction of a degree. These animals have an almost perfect 

 mechanism for the regulation of the bodily heat. With 

 a rise of temperature there is, in the mammals, an increase 

 of perspiration and an increased evaporation from the 

 surface of the body which tends to cool the blood. When 

 the temperature sinks, there is less evaporation from the 



