INTRODUCTION 199 



the limbs, as well as other parts, while in tadpoles, 

 although the tail and rudiments of hind limbs, if cut 

 off, immediately grow again, will only do so in the early- 

 stages, the power decreasing rapidly with age. 



The food of Batrachians is exclusively animal, except 

 in the larval stages. They cannot drink, but absorb the 

 necessary water through the skin. According to Donald- 

 son, some frogs, after being kept in dry air for a few hours, 

 lose about fifteen per cent, of their weight, which is re- 

 gained, when replaced in water, in under twenty-four hours. 



Batrachians cannot stand extreme heat ; to cold they 

 are not very sensitive, and species of temperate climes do 

 not show any very evident signs of distress under ice. 



The name Amphibians is frequently used to designate 

 this class of animals ; if we adopt that of Batrachians it 

 is in consideration of the fact that the former term has 

 for a long time in the past been used as a common designa- 

 tion for both Reptiles and Batrachians, for instance, by 

 Linnaeus ; when the Amphibians were first divided into 

 two classes, the name Reptilia was given to the higher 

 class, that of Batrachia to the lower. 



