MAMMALS 



191 



Fig. 340. — Walrus (Trichechus rosmarus). 



tiles have been forced into subordination, and have become 

 smaller and timid. 



Classification of Mammals. — Which two have the closest 

 resemblances in the following lists : Horse, cow, deer. Why ? 

 Cat, cow, bear. Why ? Monkey, man, sheep. Why ? Rat, 

 monkey, squirrel. Why? Giraffe, leopard, camel. Why? 

 Walrus, cat, cow. Why ? 

 Check the five mammals 

 in the following lists that 

 form a group resembling 

 one another most closely: 

 Lion, bear, pig, dog, squir- 

 rel, cat, camel, tiger, man. 

 State your reasons. Gi- 

 raffe, leopard, deer, cow, 

 rat, camel, hyena, horse, 

 monkey. State reasons. 



Teeth and toes are 

 the basis for subdividing 

 the class mammalia into 

 orders. Although the 



breathing, the circulation, 

 and the internal organs 

 and processes are 



similar in all mammals, 

 the external organs vary Fig. 341. — Weasel, in summer; in Canada 



greatly because of in winter " is a11 white but tip of tai1 ' 



the varying en- 

 vironments of different species. The internal structure 



enables us to place animals together which are essentially 

 alike ; e.g. the whale and man are both mammals, since 

 they resemble in breathing, circulation, and multiplication 

 of young. The external organs guide us in separating the 

 class into orders- The teeth vary according to the food 



