XX. FROGS, TOADS, AND SALAMANDERS 



Chordata {continued) 



ijass III. — Amphibia, (animals ivith double lives), (amphi, 

 doul^le; bios, life) 



As a class, the amphibians, of which there are over a 

 thousand known species, present a great diversity of forms. 

 No general statement can be made regarding this class of 

 animals to which exception cannot be found. The great 

 majority of the amphibians possess legs and have smooth 

 skins — not covered with scales like the snakes and lizards. 

 A typical amphibian Uves a double life, as it were. It 

 begins hfe in the water, in the form of a fishlike animal 

 without legs but with a large tail and a pair of external 

 gills. Later, the gills are replaced by lungs, the tail is 

 absorbed into the body, and four functional legs appear. At 

 this stage of its existence one species of amphibian may 

 live on land while another species may confine itself wholly 

 to an aquatic life. 



An Example of the Class — the Green Frog 



The body. — The body of the frog is short and wide and 

 without a tail. It is divided into two regions only, — the 

 head and the trunk. Like the perch, there is no distinct 

 neck, yet there is one neck vertebra between the head and 

 trunk which shows that the neck of the higher vertebrates 

 is just beginning to make its appearance in the frog. The 



229 



