54 VERTEBRATES I MAMMALS. 



length of twenty feet, and is covered with short brown 

 hair. It uses its strong tusks to lift itself from the 

 water upon the rocks or ice-banks, where large numbers 

 bask together in the sunshine. The tusks also serve as 

 means of defence, and for obtaining sea-weed, which with 

 fish constitutes its food. When attacked it is fierce, and 

 becomes a formidable antagonist, especially if attended 

 by young. It readily smashes a boat with its tusks, or, 

 rising in the water, hooks them over the side, and upsets it. 



SUB-SECTION VI. 



THE ORDER OF MARSUPIALIA, OR MARSUPIALS. 



The Order of Marsupialia comprises animals whose 

 special characteristic is that their young are brought forth 

 in an exceedingly premature state of development, and, in 

 most instances, are received into a peculiar pouch on the 

 abdomen of the mother, where they are nourished till 

 they have acquired a degree of development correspond- 

 ing to that in which other mammals are born. The 

 young, after they are able to walk, also resort to the 

 pouch of the mother for safety in times of danger. With 

 the exception of one family found in America, the Marsu- 

 pials are all confined to Australia and islands immediately 

 adjacent ; and it is a singular fact, that all the mammals 

 of Australia, over a hundred species of which are known, 

 belong to this order. 



DIDELPHID^, OR OPOSSUM FAMILY. This Family 

 comprises all the Marsupials of North and South Amer- 

 ica, and is peculiar to this continent. Opossums are 

 mostly small animals, the largest scarcely exceeding the 

 common cat, and the smallest but little larger than a 

 mouse. They are plantigrade and five-toed. The dental 

 formula is, incisors ^, canines ^, premolars ^, molars 

 ^- 4 . Their food consists of birds, birds' eggs, insects, and 



