WHAT AMPHIBIAN MEANS 3 



Anatomically, the rule is that amphibians have no 

 such complete ribs as are found in the other classes. 

 Externally, it may be said in a general way of those 

 living now, that amphibians are naked-skinned, rep- 

 tiles are scaly, mammals have hair and birds have 

 feathers. Some reptiles, however, are not, and a few 

 mammals are scaly. 



Fig. 1. — Frog (Discogtossus pictus) in action, showing free develop- 

 ment of limbs as compared with other members of its class. 



Likewise many extinct amphibians and reptiles 

 had paddle-shaped limbs. Their structure, however, 

 shows that these were not true fins, but were made 

 out of a true three-jointed leg. Likewise some of 

 each of these classes have no legs at all, but they are 

 readily distinguished by the other characters noted. 



Amphibians were once classed with reptiles, be- 



