﻿6 ALLENS NATURALISTS LIBRARY. 



cause of this universal extinction (for universal it is) of tlie 

 most gigantic Mammals throughout the world soon after man 

 made his appearance on the earth, is one of those problems 

 which has not yet received a satisfactory answer, as not even a 

 glacial period could have made a clean sweep of the whole 

 globe. 



Having said thus much as to the general distribution of the 

 Marsupials, we naturally turn to the consideration of what 

 constitutes a Marsupial, or in what respects the group differs 

 from other members of the Mammalian class. Since these 

 animals derive their names from the presence of the well- 

 known pouch or marsupium in which the young of so many 

 species are carried, it would be not unnatural to suppose that 

 the presence of this pouch would constitute the chief dis- 

 tinctive feature of the whole group. Unfortunately, however, 

 the pouch is wanting in certain representatives of the assem- 

 blage, and we have accordingly to rely on other characteristics 

 in order to define a Marsupial. Such a characteristic is to be 

 found in the extremely imperfect state of development in 

 which the young are brought forth ; these being in fact little 

 more than helpless and almost motionless lumps or sacs of 

 flesh, which are exceedingly small in relative size to their 

 parents, the new-born young of the Great Red Kangaroo being 

 not larger than a man's thumb. At birth, these imperfectly- 

 developed young are transferred to the teats of the feniale 

 parent, where they hang suspended by the aid of special 

 grasping muscles in their thick and nearly circular lips. They 

 are, however, quite unable to suck by themselves, and the 

 milk is consequently injected down their throats by means 

 of a muscle which has the pov/er of compressing the mam- 

 mary gland. In all members of the group the teats are 

 situated on the abdomen, and they are generally placed 

 within that pouch or marsupium^ from which the order takes 



