tiles have been forced into subordination, and have become smaller and timid.
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Fig. 340.—Walrus (Trichechus rosmarus).
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, dog, squirrel, cat, camel, tiger, man. State your reasons. Giraffe, leopard, deer, cow, rat, camel, hyena, horse, monkey. State reasons.
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Fig. 341.—Weasel, in summer; in Canada in winter it is all white but tip of tail.
Teeth and toes are the basis for subdividing the class mammalia into orders. Although the breathing, circulation, and internal organs and processes are similar in all mammals, the external organs vary greatly because of the varying environments 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
