300 ELEMENTARY ZOOLOGY 



United States and in the Mississippi valley. It is green- 

 ish in color with the head usually bright pale green. Its 

 croaking is very deep and sonorous. The pickerel-frog 

 (R. palustris], which is bright brown on the back with two 

 rows of large oblong square blotches of dark brown on 

 the back, is found in the mountains of eastern United 

 States. The little pale reddish-brown wood-frog (R. syl- 

 vaticd) with arms and legs barred above is common in 

 damp woods and is "an almost silent frog." The 

 peculiar and infrequently seen frogs known as the ' * spade- 

 foots ' ' (Scaphiopus} are subterranean in habit and usually 

 live in dry fields or even on arid plains and deserts. 

 They pass through their development and metamorphosis 

 very rapidly, appearing immediately after a rain and lay- 

 ing their eggs in temporary pools. At this time of egg- 

 laying they utter extraordinarily loud and strange cries. 

 Some frogs in other parts of the world live in trees, and 

 the eggs of one species are deposited on the leaves of 

 trees, leaves which overhang the water being selected so 

 that the issuing young may drop into it. 



The true tree-frogs or tree-toads (Hylidae) constitute a 

 family especially well represented in tropical America. 

 They have little disk- or pad-like swellings on the tips of 

 their toes to enable them to hold firmly to the branches 

 of the trees in which they live. Some, like the swamp 

 tree-frog and the cricket-frog, are not arboreal in habit, 

 remaining almost always on the ground. The common 

 tree-frog of the eastern States (Hyla vcrsicolor) is green, 

 gray, or brown above with irregular dark blotches, and 

 yellow below. It croaks or trills, especially at evening 

 and in damp weather. Pickering's tree-frog (Hyla 

 pickeringii} makes the "first note of spring" in the 

 eastern States. This tree-frog is the one most frequently 

 heard in the autumn too, but "its voice is less vivacious 

 than in the spring and its lonely pipe in dry woodlands is 



