CHAPTER XVIII 

 SUBPHYLUM VERTEBRATA: CLASS IV. AMPHIBIA 



THE common amphibians are the frogs, toads, and salamanders. 

 They spend part or all of their existence in the water or in 

 damp places. Most of them lay their eggs in the water, and 

 the larvae, which breathe with gills, are known as tadpoles or 

 pollywogs. Some amphibians are often confused with reptiles 

 (especially with the lizards) because of their similarity of form, 

 but almost all reptiles possess scales, whereas amphibians have 

 usually a smooth, slirpy skin without sca ilps except in a few rare 

 species. There are two orders of extinct amphibia and three 

 orders of living forms. The latter are as follows : 



Order i. APODA. The APODA or CCECILIANS are legless, 

 worm-like amphibians inhabiting tropical and subtropical 

 regions. 



Order 2. CAUDATA. These are amphibians with tails. They 

 include the mud-puppies, sirens, and salamanders. 



Order 3. SALIENTIA. The tailless AMPHIBIA, frogs and 

 toads, belong to this order. 



i. THE FROG 



The leopard frog, Rana pipiens, lives in or near fresh-water 

 lakes, ponds, and streams, and is distributed over the North 

 American continent except on the Pacific -slope. The frog leaps 

 on land and swims in the water. The hind legs are large and 

 powerful. When the frog is on land they are folded up, and 

 a sudden extension propels the body through the air. Like- 

 wise in swimming the hind legs are alternately folded up and 



477 



