THE FROG 329 



that extend their range along the Andes south of the Equator. 

 North America is especially rich both in species and individ- 

 uals of Urodela. Those which lose the tail in the adult stage, 

 like the frogs, are called the Anu'ra. These are found in all 

 parts of the world, es]Decially in South America and Australia. 

 A third group (Gym'noph iona) , which is found only in the tropics, 

 contains animals that have a worm-like body, live in the ground, 

 and have more or less rudimentary eyes. It will be seen that 

 the Amphibia are found chiefly in tropical and subtropical 

 countries, although a large number thrive in colder parts of the 

 temperate zone. 



As an example to illustrate the structure of Amphibia we 

 may take the frog. 



General Form of the Body. — The frog is not a typical am- 

 phibian, since it has lost its tail, so that only head and trunk re- 

 main, and the anal opening lies at the very hind end of the 

 body. The appendages have become long and slender as 

 compared with those of the fish, and five distinct toes are 

 present on each foot. The whole Ijody is covered with a 

 delicate skin devoid of scales such as fishes have, or other 

 outgrowths „and coverings of the skin such as are found in 

 birds and mammals. The skin contains abundant glands, 

 however, the secretions of which may be poured over the 

 skin to protect it from drying up. 



The Skeleton of the frog consists of an axial and an appen- 

 chcular part (Fig. 311). The vertebral column consists of a few 

 simple vertebrae, to each of which a pair of short ribs is fused. 

 The skeleton of the rudimentary tail is represented by a long, 

 bony rod.' The skull is simple as compared with that of the 

 fish, partly because of the absence of gills and partly because 



1 Urostyle, UST., Fig. 311. 



