CHAPTER XXII 

 TOADS, FROGS AND SALAMANDERS 



The toads and frogs are the most common representatives 

 of the class Amphibia, but the salamanders, or water-dogs, 

 are very often found along streams or in moist places. The 

 coecilians, legless, worm-like or snake-like creatures occurring 

 in the tropics, also belong to this class. 



Almost fifteen hundred living species of amphibians are 

 known. These may be grouped into three fairly well-defined 

 orders, the Apoda, or footless, snake-like forms, the Urodela, 

 or tailed amphibians, and the Anura, or tailless forms like the 

 toad and frog. 



The Coecilians (order Apoda). This order includes a few 

 worm-like or snake-like footless species called ccecilians usu- 

 ally having small scales embedded in the skin. They occur 

 only in tropical regions and are of no economic importance. 



The Water-dogs (order Urodela). 'Several widely different 

 forms are grouped together in this order so that it is often 

 divided into suborders. They all agree in having a tail, which 

 may be longer or shorter than the rest of the body. The mud- 

 puppies or water-dogs, genus Necturus, occur in the rivers and 

 lakes of the northern United States. They attain a length of 

 about two feet when full grown. They have four legs, and 

 breathe by means of bushy gills which arise from in front of 

 the forelegs. The sirens or mud-eels, genus Siren, burrow in 

 the mud in ponds and ditches in the southern states, attaining 

 a length of about three feet. They have three pairs of gills 

 and only one pair of legs. 



The large, heavy-bodied, blackish water-dog or hell-bender, 

 genus Cryptobranchus, is another aquatic form, but the ex- 

 ternal gills are replaced by small openings or gill slits which 

 lead into the throat. It is found along the Ohio river 



256 



