228 BRANCH CHORDATA 



also an exception. That cloudy or damp weather has some 

 effect in making certain species, as the. tree-frogs, sing, is per- 

 haps explained by the fact that the skin of amphibians is used as 

 a breathing organ as well as for a body covering, and it must be 

 kept moist to be serviceable. 



Influence of Temperature. — Amphibians living in the water 

 assume its temperature, which varies much from noon to mid- 

 night, and from the stream in open sunshine to the cool, shady 

 spring. According to Gadow, "most Anura die when their tem- 

 perature rises to 40° C," but those outside of water in open air 

 endure gr(>;itcr heat than aquatic ones, since the evaporation of 

 the moisture from their skin lowers their temperature. Most 

 of them, and especially the drier skinned toads, seek the cool 

 shade or even estivate during the hottest part of the summer. 

 Many of them, unless they arc used to tropical climates, can en- 

 dure a very great amount of cold, their temperature sometimes 

 falling to the freezing-point during hibernation. Our spotted sal- 

 amander, in a jar of water out-doors, was forgotten one severely 

 cold night, when the water about it froze solid. It was put into 

 a cool room and allowed to thaw gradually as the weather moder- 

 ated, after which the salamander seemed to be as active as ever. 

 Of course, the animal was not sawed into parts to find out if 

 it was frozen solid, but it surely looked solid enough. It does not 

 seem possible that the heart was absolutely frozen, for the heart 

 "must not itself be frozen if the animal is to have a chance of 

 recovery."' 



CLASSIFICATION OF AMPHIBIA 



Order I. Stegoceph'ala. — This is an extinct order of amphibians, 

 described by Scott as animals, which have a skull "well covered 

 with a roof of sculptured bones and which are of moderate or 

 small size, not exceeding 7 or 8 feet in length and mostly much 

 smaller. The backbone is not ossified, the limbs are weak, the 

 tail short and broad, and in many forms the belly is protected 

 by an armor of bony scutes."^ Most of them were like sal- 

 amanders in shape, but some were long and snake-like. 



Order II. Ap'oda or Gymnophi'ona. — This group comprises 



one family of limbless, tailless, A-ermiform, subterranean am- 



1 Gadow, p. 68. 



^ Scott, "Introduction to Geology,'' p. 427. 



