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 

 each other most closely : 

 Lion, bear, pig, clog, 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, circulation, and 

 internal organs and pro- 

 cesses are similar in all 

 mammals, the external 

 organs vary greatly be- 

 cause of 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 



Fig. 341. — Weasel, in summer; in Canada 

 in winter it is all white but tip of tail. 



