AMPHIBIANS 



327 



In amphibians, as in all animals above them, there is 

 not only a vertebral colurnn, but there are four limbs, 

 the hard parts of which are parts of the bony skeleton. 

 The fore legs of the frog are small, and have four toes 

 each; the hind legs are long and strong, and each has 

 five webbed toes. The hind legs are, therefore, well 

 adapted for both jumping and swimming. 



The frog's body (Fig. 268) is covered with a colored 

 skin, the outer layer of which it sheds in moulting. Each 



Gills 



FIG. 268: 

 Stages in the Development of a Frog. 



of the frog's eyes is closed by an upper and a lower lid; 

 but the lower is the more movable. Back of the eyes, on 

 the sides of the head, are two membranes ; these form the 

 outer ears. 



The blood of amphibians, like that of fishes, is low in 

 temperature: these animals are "cold blooded." The 

 heart has two receiving chambers (a right and a left auricle) 

 and one ventricle. This is an advance beyond fishes 

 (cf. 341). 



