190 



Descriptive Zoology. 



of the body and swims by the sidewise movements of the 

 tail. At this time the intestine is long and coiled spirally. 

 Then for a time the tadpole quits eating. It fasts, but is 

 maintained by the material from its tail, which is being 

 absorbed while a. great transformation is taking place. The 

 horny lips and jaws are shed, the mouth becomes wider and 

 develops true jaws with teeth. The long, coiled intestine 

 becomes relatively short. The anterior limbs are pushed 

 out through the fold of the skin that inclosed them. Lungs 

 are developed, although they are at first but little used, the 

 tadpole coming to the surface occasionally to get a mouth- 

 ful of air; respiration is still chiefly accomplished by the 



Gills 



FIG. 120. THE SIREN; MUD EEL. 



Gills persistent. 



gills, but the lungs come to be used more and the gills less 

 until finally the gills disappear. It was herbivorous ; now 

 it is carnivorous. Formerly strictly aquatic, it is now am- 

 phibian. In short, our tadpole has become a frog. 



CLASSIFICATION OF AMPHIBIA. 



The Siren. The lowest of the amphibians is the siren 

 or mud eel. It is eel-like in form, having gills that persist 

 through life, and one pair of legs (the anterior). It lives 

 in the swamps of the Southern states and sometimes is 

 three feet long. 



