178 ANIMAL FORMS 



mers and leapers, and thus equipped they hereafter lead a 

 wholly terrestrial or seniiaquatic life. 



170. Distribution and common forms. All the Amphibia 

 are dependent upon moisture. Almost all are hatched and 

 developed in fresh water, and those which leave the water 

 return to it during the breeding season. So we find repre- 

 sentatives of the group all over the world having much the 

 same range as the fresh-water fishes. The great majority 

 of the salamanders are confined to the northern hemisphere, 

 but the toads and frogs are almost universally distributed. 



Among the salamanders in this country only a relatively 

 few species completely retain their external gills. This is 

 the case with sirens and mud-puppies or water-dogs (Fig. 

 110), which may occasionally be seen in the clear waters 

 of our lakes and rivers crawling slowly about in search of 

 food, and every now and then rising to the surface to gulp 

 in air. The remainder lose their gills more or less com- 

 pletely, and usually leave the water for damp haunts on 

 land. One of the blunt-nosed salamanders, known as the 

 tiger salamander (Amblystoma tigrinunt), is found in moist 

 localities in most parts of the United States. Besides these 

 are numerous small species, among them the newts (Die- 

 myctylus)) ranging widely over the United States, living 

 under logs and stones and feeding upon the small insects 

 and worms inhabiting such situations. In several species 

 of salamanders the lungs disappear with age, and respira- 

 tion is performed solely through the surface of the skin. 



The tailless amphibians are much more abundant and 

 familiar objects than the salamanders, and from the open- 

 ing of spring until late in the fall they are met with on 

 every hand. With few exceptions the frogs live in or about 

 ponds and marshes, in which they obtain protection in 

 troublous times and from which they derive the store of 

 worms and insects that serve as food. On the other hand, 

 the tree-frogs, as their name indicates, usually abandon the 

 water and repair to moist situations in trees and other vege- 



