AMPHIBIANS 157 



well developed and attached in front, the hinder end being free so that 

 it can be thrown forward; it is in this manner that the animal captures 

 the insects and other small animals on which it feeds. The eggs are 

 usually laid in the water and the tadpoles which emerge from them have 

 external integumental gills and a swimming tail, but no legs. In the 

 metamorphosis which follows, the gills and tail are absorbed, the legs 

 and lungs develop, the head and mouth change their- form and rela- 

 tive size, and the animal becomes adult and fitted for a terrestrial life. 



--3 



Fig. 81. — Upper surface of head of Bufo americamis: i, cranial crests; 2, tympanum; 

 3, parotoid glands (after Surface). 



About 1,600 species of Salientia are known, which occur in all the 

 geographical regions of the earth, about 60 species being in the United 

 States, grouped in 6 families. 



On the Identification of the Salientia. — The descriptions of frogs 

 and toads in this book apply to both adults and larvae, and inasmuch as 

 the animals in these two stages of development differ radically in 

 form and appearance, the descriptions of the two stages are given 

 separately. 



I. The Adult. — There is a general uniformity in the shape of the 

 body of the various species of frogs and toads, and the most important 

 descriptive features are the following; the length in millimeters and 

 color of the body, the size and shape of the head, the length of the hind 

 legs, the character of the digits, the number of which is four in the 

 fore foot and live in the hind, the character of the skin, ■vy'hether it 

 is smooth, tubercular or warty, the presence and character of the paro- 

 toid gland, the tympanum and the teeth. For a complete analysis of 



