THE BIOLOGY OF THE FROG 



those of many cave animals, are rudimentary. Its color is 

 nearly white, but if exposed to light its skin gradually turns 

 dark and eventually may become nearly black. 



A cave salamander, Typhlomolge rathbuni, closely allied 

 to Proteus, was found only a few years ago in Texas, where 

 it was discovered in water thrown up from an artesian well. 

 The body of this species is slender and provided with a long, 

 flattened tail. The legs are long and slender. The eyes, 

 Hke those of Proteus, are rudimentary and buried beneath 

 the skin. The most common representative of the Proteidae 



Fig. I. — Proteus angubms. Front view of the mouth in the upper left 

 corner. (Atter Gadow, Cambridge Natural History.) 



are the "mud puppies" or "water dogs," which belong 

 to the genus Necturus. Necturus maciilosus is the most 

 abundant species. It occurs in the northern and eastern 

 part of the United States, west of the x-Xlleghanies, and is 

 especially abundant in the region of the Great Lakes. Its 

 general color is brown above, marked with darker spots, and 

 a dirty white or dusky color below. It has bushy red gills, 

 which are kept moving back and forth at frequent intervals. 

 Like most amphibians, it is most active at night ; during the 

 day it lies concealed out of the reach of hght. 



The family Sirenidae is represented by two genera. Siren 

 and Pseudobranchus, both of which are confined to North 



