AMPHIBIA (BATRACHIA) 



127 



the Hylidae or treefrogs, the Ranidae or true frogs and the Bufonidae 

 or toads. 



The Hylida, Fig. 90, are usually small forms; they are arboreal in 

 habits, as the name indicates, and as an aid in climbing have adhesive 

 disks at the ends of their fingers and toes. They have remarkable 

 vocal powers, due partly to the presence of a large vocal sac. Of the 

 nearly 200 species, more than a dozen are found in North Am- 



PIG. 90. Tree frog, sp. Xi. Note discs on toes. 



erica. Though doubtless of less importance than the other Anura, 

 these small frogs probably destroy large numbers of harmful insects. 



The Ranidce, of which there are more than 250 species, more than 

 a dozen of which occur in the United States, are useful as destroyers 

 of insects, as subjects for dissection and experimental work, and es- 

 pecially as an article of diet. 



Almost any of the true frogs may be used as food, though many people 

 think that only the bullfrogs are edible. A simila r mistaken idea pre- 



