FIG. 237. The green frog, showing the tympanic 

 membrane (ear drum) just back of the eye. Pho- 

 tograph half natural size by Overton. 



AMPHIBIA 205 



adult stage they are provided with lungs, but respiration 

 is carried on to a large extent through the skin, especially 

 in the frogs spend- 

 ing much time under 

 the water. 



The bull frog 

 (Rana catesbiana) is 

 the only amphibian 

 much valued for 

 food. The length of 

 a full-grown speci- 

 men from the tip of 

 the nose to the end 

 of the outstretched 

 hind legs is nearly two feet. It may be distinguished from 



the other frogs by the 

 fact that the web of the 

 foot reaches to the tip of 

 the fourth toe and the 

 back is of a greenish color 

 with small faint dark 

 spots. Thousands of dol- 

 lars' worth of frogs' legs 

 are sold annually in the 

 city markets. The green 

 frog (Rana clamitans) is 

 characterized by a tym- 

 panic membrane larger 

 than the eye and the 



FIG. 238. The common tree frog two thirds 



natural size. Photograph was taken just presence of a fold OH 

 after it was transferred from a sheet of 



white paper. Twenty minutes later it was pitViPr csirlp nf 

 the same color as the oak bark. 



