THE ORDER AMONG ANIMAL TYPES 



119 



Sharks, Lampreys, and Whales (which are Mammals) are often 

 mistakenly called fishes. 



Class IV. AMPHIBIA (Fig. 69). Frogs, Toads, and Salamanders. 

 The young are aquatic, the 

 eggs being laid in water, ex- 

 cept in some unusual forms 

 that live in dry environments. 

 None of the present-day 

 Amphibia ever have scales. 



Class V. REPTiLiA (Fig. 70). 

 Snakes, Lizards, Turtles, 

 Crocodiles. The eggs are laid 

 ©n land, although the adult 

 may be adapted to live in the 

 water. The skin is usually 

 scaly. Members of this and of 

 the class Amphibia are fre- 

 quently confused, although 

 the distinction is quite clear. 



Class VI. AVES (Fig. 71). 

 The Birds. Only this class and 

 the class Mammalia are 

 warm blooded. Members of 

 the class Aves are character- 

 ized by wide changes from 

 the usual vertebrate structure 

 as a consequence of their 

 adaptation for flight. The 

 body is covered with feathers, 

 which are highly modified scales. The forelimbs are modified for 

 flight (Fig. 212). 



Class VII. MAMMALIA. Have a hairy covering at some time in their 

 life cycle. The young are nourished by the secretion of certain modi- 

 fied skin glands termed mammae. There are three sub-classes: 



FIG. 70. TURTLE 

 Fig. 70. — A common turtle, representa- 

 tive of the class Reptilia. Compare with 

 Fig. 69 and with Fig. 71, particularly as 

 regards beak and claws. 



