258 FIRST LESSONS IN ZOOLOGY 



best known of the foreign marsupials. The members of 

 this order are cliaracterized by the birth of the young 

 while very small and incompletely developed, and the 

 transference of the )-oung to an external pouch, the mar- 

 supium, in which they are carried for a longer or shorter 

 time. The opossum lives in trees, is about the size of a 

 common cat, and has a dirty-yellowish woolly fur. Its 

 tail is long and scaly, like a rat's. Its food consists 

 chiefly of insects, although small reptiles, birds, and bird's 

 eggs are eaten. When ready to bear young the opossum 

 makes a nest of dried grass in the hollow of a tree, and 

 produces about thirteen very small (half an inch long) 

 helpless creatures. These are then placed by the mother 

 in her pouch, where each clings to a teat. Here they re- 

 main until two months or more after birth. Probably all 

 the North American opossums, found from New York to 

 California, and especially common in the Southern States, 

 belong to a single species, but there is much variety 

 among the individuals. 



The rodents or gnawers (Glires). — The rabbits, por- 

 cupines, gophers, chipmunks, beavers, squirrels, and rats 

 and mice compose the largest order among the mammals. 

 They are called rodents or gnawers (Glires) because of 

 their well-known gnawing powers and proclivities. The 

 special arrangement and character of the teeth are char- 

 acteristic of this order. There are no canines, a tooth- 

 less space being left between the incisors and molars on 

 each side. There are only two incisor teeth in each jaw 

 (rarely four in the upper jaw), and these teeth grow con- 

 tinuously and are kept sharp and of uniform length by 

 the gnawing on hard substances and the constant rubbing 

 on each other. The food of rodents is chiefl\' vegetable. 



Of the hares and rabbits the cottontail {Lcpiis iiuttalli) 

 and the common jack-rabbit (A. cainpcstris) arc the best 

 known. The cottontail is found all over the United 



