THE AMPHIBIA 



303 



The green frog 

 lives in eastern 

 North America. 

 It can be distin- 

 guished from the 

 bullfrog by the 

 presence of two 

 folds of skin along 

 the sides of the 

 back (Fig. 181). 



The tree frogs 

 (Fig. 182) are 

 often erroneously 

 called tree toads. 

 They have adhe- 



FIG. iSi. Green frog. (Photo, of living animal 

 furnished by American Museum of Natural History.) 



sive disks on their toes and fingers, which enable them to climb 

 trees, and are provided with large vocal sacs which give them 



a correspondingly 

 loud voice. 



The common tree 

 frog is about two 

 inches long. It has 

 the power of slowly 

 changing its color 

 so as to produce a 

 perfect harmony 

 between itself and 

 its surroundings. 

 These colors are due 

 to pigments in the 

 skin, usually brown, 

 black, yellow, or red, 



FIG. 182. Tree frog. (Photo, of living ani- 

 mal furnished by American Museum of Natural 

 History.) 



which are contained in cells called chromatophores (Fig. 184). 

 The power of changing its colors is possessed by most Amphibia, 

 but especially by the tree frogs. The black chromatophores are 



