282 AN INTRODUCTION TO ZOOLOGY. 



of tlie Opossums, some tree-climbiBg marsupials, in 

 which the pouch is not so well developed as that of 

 others of the group, carry their young about in a 

 singular manner : the tail is prehensile, and the young 

 curl their tails round that of the mother, and thus 

 ride about securely on her back. Other marsupial 

 mothers sometimes carry the young about on their 

 backs, but do not possess so convenient a way of 

 making them safe. 



The marsupial animals are of very different kinds, 

 having become modified with a view to their food 

 habits, so that they mimic other groups of animals. 

 Thus there are marsupial Carnivora, which resemble 

 the true Carnivora in the shape of their teeth and 

 skull; and marsupial rats, which are very like the 

 true rodents in appearance, and marsupial herbivora 

 and insectivora. (See figs. Ill, 114, 121.) The Mar- 

 svpialia used to be looked upon merely as one of the 

 orders of the Mammalia ; but they are now understood 

 to differ so widely from the higher Mammalia, that 

 they are sometimes made into a group called Me- 

 TATHERiA, divided into sub-groups according to the 

 differences of structure just spoken of, while the 

 orders of the higher Mammalia are classed under an- 

 other group called Edtheeia. The Monotremes are 

 then distinguished as Peotothekia. This classification 

 is largely based on the structui-e of the reproductive 

 organs : the names Oenithodelphia, Didelphia, and 

 MoNODELi'HiA, are also used as equivalents of the 

 names just given, to indicate respectively the Mono- 



