MAMMALIA 



619 



Order Marsupialia. — This group of mammals has no well-developed 

 placenta and is sometimes designated as a separate subclass, called 

 Metatheria. Their shell-less eggs absorb food from the wall of the 

 Icterus. The young are born in a very immature state and make their 

 way to the marsupial pouch where they cling to the teats and are 

 nourished on milk until they can shift for themselves. The group is 

 at its best in Australia and nearby islands. Here is found the true 

 kangaroo with its short, poorly developed forelimbs, powerful hind- 

 limbs and tail, and peculiar upright posture and leaping locomotion. 

 The seven families of the order include not only kangaroos, but 

 also opossums, phalangers, wombats, bandicoots, dasyures, and Caeno- 

 lestes. There are several species in South America. Some of these 

 are no larger than mice or rats and are frequently brought into this 

 country on bunches of bananas. In the United States, the opossum, 

 Didelphis virginiana, is the only representative of the group. It is 

 about the size of the common cat, with a long scaly tail and fur of 

 dirty yellowish white color. Ten or twelve young are born at a time 

 and are carried in the pouch of the mother. The young remain with 

 the mother about two months, often riding as a group on the mother's 

 back during the latter part of this period. The opposum is quite 

 active at night, but it usually sleeps through the day. 



Order Insectivora. — This group includes the common mole, Scalopus 

 aquaticus, the hairy-tailed mole, Parascalops Ireweri, the star-nosed 

 mole, Condylura cristata, the shrews and short-tailed shrews. They 

 are quite well distributed through North America and Europe, but 

 are absent from Australia and most of South America. The group 

 is largely burrowing and nocturnal in habit. They feed chiefly on 

 insects which they seize with their sharp, projecting incisor teeth. 

 The moles are well adapted to the burrowing habit of life. They 

 have rudimentary eyes, no external ears, short stout forelimbs with 

 strong sharp claws for digging. Their tunnels are just under the 

 surface of the saaidy loam in which they live. They occasionally 

 throw up molehills along the tunnel. 



The shrews are small, mouselike animals with conical, pointed 

 heads, ratlike feet, small eyes, and external ears. They may live 

 in burrows or on the surface of the ground under logs, rocks, or 

 heavy vegetation. The long-tailed shrew, Sorex personatus, of the 

 North and the East, and the short-tailed shrew, CryptoUs parva, ex- 



