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ECONOMIC ZOOLOGY 



scarcely be said to have any economic value, except, perhaps, in the 

 determination of geological horizons. As in other groups the classifica- 

 tion of the Amphibia varies with different authors; the extinct forms are 

 usually placed in two or three orders, the living forms in the following 

 three orders: i. Apoda or Gymnophiona are legless, snake-like or worm- 

 like forms found chiefly in the tropical and subtropical countries; 2. 



FIG. 86. Metamorphosis of the frog. Tadpoles in different stages of develop- 

 ment, from those just hatched (i) till the adult form is reached (8). 1-3, about 

 life size; 2a, enlarged; 4-8, somewhat reduced. (From Hegner, College Zoology, 

 after Mivart.) 



Caudata or Urodela are the tailed Amphibia, such as mud-puppies, sala- 

 manders, etc.; 3. Salientia or Anura are the tailless forms, the frogs and 

 toads. Of these three orders the last is by far the largest and the first 

 the smallest. In cold regions the amphibia hibernate through the se- 

 vere winter weather by burying themselves in the ground or in the mud 

 and leaves at the bottom of ponds and streams. Being inoffensive 



