18 THE BIOLOGY OF THE FROG chap. 



and where they undergo development as far as the tadpole 

 stage. 



The Engystomatidae contain but one North American 

 species, Engystoma carolinense, which is found in the South- 

 ern States, from South Carolina to Texas. The large family 

 Cystignathidae is represented on this continent by only three 

 species, which are confined to Mexico and Florida. 



The Ranidae, or true frogs, include the Firmisternia with 

 cylindrical sacral diapophyses. The family comprises nu- 

 merous genera, only one of which, the typical genus Rana, 

 is found in North America. This genus contains about 

 one hundred and forty species, which are found in all of 

 the continents of the globe, although occurring only in the 

 extreme northern parts of South America and Australia. 

 There are fourteen North American species, two of which, 

 R. temporaria and R. agi/is, occur also in Europe. Only a 

 few of the better-known forms are here treated of. Full 

 description of the species may be found in Cope's " Batrachia 

 of North America." 



Rana catesbiana, the bullfrog. — This is by far the largest 

 of North American species of Rana, and one of the largest of 

 the genus. It attains a length of five to eight inches. It is 

 widely distributed throughout the United States, east of the 

 Rocky Mountains, from Mexico to Canada. The color of 

 the upper surface varies from green to olive-brown, marked 

 with small darker spots. The head is usually bright green, 

 and the legs are marked with blotches of darker color. 

 The dermal plicae behind the eyes are indistinct. The tym- 

 panum is very large, especially in the male. The toes of 

 the hind feet are broadly webbed, the web extending to the 

 tip of the fourth toe. 



This species rarely goes far from the water. It is usually 

 found either partly immersed in the water or sitting on the 



