178 ANIMAL FORMS 
mers and leapers, and thus equipped they hereafter lead a 
wholly terrestrial or semiaquatic 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 (Amédlystoma tigrinum), 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- 
