FISHES, BATRACHIANS, AND REPTILES 219 



but elongate and slender and tailed. Their life-history is 

 like that of the frogs, although some salamanders which 

 live on land (they are to be found under logs and stones 

 in the woods) produce their young alive. To compare the 

 external structure of a salamander with that of a frog or 

 toad one of the tiger salamanders or one of the little tri- 

 tons or efts, common all over the country, should be used. 

 The little green triton or eft of the Eastern States, or 

 its larger brown-backed congener (fig. 177) of the Pacific 

 coast, is common in water, while another eft, the little 

 red-backed salamander, is common in the woods under 

 logs and stones. 



The reptiles. — The class of reptiles includes the liz- 

 ards, snakes, tortoises, turtles, crocodiles, and alligators. 

 They are cold-blooded and breathe for their whole life 

 exclusively by means of lungs, the forms which live 

 in water coming to the surface to breathe. They are 

 covered with horny scales or plates, which with the en- 

 tire absence of gills after hatching readily distinguish 

 them from all the batrachians. While most reptiles live 

 on land, some inhabit fresh water and some the ocean. 

 As the young have the same habitat and general habits 

 as the adult, there is no such metamorphosis in their 

 life-history as is shown by the batrachians. The reptiles 

 are widespread geographically, occurring, however, in 

 greatest abundance in tropical regions, and being wholly 

 absent from the arctic zone. They are not capable of 

 such migrations as are accomplished by birds and many 

 mammals, but withstand severely hot or cold seasons by 

 passing into a state of suspended animation or seasonal 

 sleep or torpor. 



The chief variations in body-form among the reptiles are 

 manifest when a turtle, lizard, and snake are compared. 

 In the turtles (fig. 178) the body is short, flattened, and 

 heavy, and provided always with four limbs, each termi- 



