16 



NATURAL HISTORY OF VERTEBRATE ANIMALS 



confined rather closely to the vicinity of water. The " leopard 

 frog," R. pipiens, on the other hand, may wander far from water 

 and thus is sometimes called the " grass frog " when found in 

 meadows. The " pickerel frog," R. palustris, may also wander 

 from the water, although it lives mostly in spring beds and in cool, 

 damp places. A more extreme example is the " wood frog," R. 

 sijlvatica^ which is regularly found in damp woods. In New Eng- 

 land this frog is common in beech woods, often a long distance from 

 water. Like the toad, it must come to the water at the breeding 

 season, and in wet weather it has access to temporary ponds. 



^^^^ff^..M^i 



Fig. 8. — The common tree frog, Hyla versicolor, showing mottled ('oloratiou 

 that matches its backgrounds in nature. 



(From Dickerson, "Frog Book," copyright, 1920, by Doubleday, Page & Co., reprinted 

 by permission.) 



Acris gryllus, the " cricket frog," is another pond and stream- 

 dwelling species, occurring often in swampy places and in small 

 bodies of water. Hyla versicolor, the " tree frog " (Fig. 8), comes 

 to the water in numbers only at the breeding season, and at other 

 times frequents damp places, chmbing tree trunks to feed upon 

 insects. Its changes in color to match the background are re- 

 markable in their rapidity and diversity, and probably account for 

 the fact that these animals are difficult to locate ; although their 

 presence is often made known by their croaking, particularly under 

 stimulation by the moist atmosphere preceding rain. 



The general distribution of Amphibia is, therefore, conditioned 

 by certain peculiarities of the body surface that have been de- 

 scribed. They cannot live in arid regions or in regions where 

 the ground remains frozen throughout the year, because they must 

 hibernate during cold weather. They are, so to speak, tied to the 

 water by the nature of their organization and activities and by 



