6 LLOYDS NATURAL HISTORY, 
cause of this universal extinction (for universal it is) of the 
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 thana man’s thumb. At birth, these imperfectly- 
developed young are transferred to the teats of the female 
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 power 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 
