10 LLOYD’S NATURAL HISTORY, 
intimately connected with one another that any such sub- 
division is impracticable; and the most that can be done in 
this way is to divide the Order Marsupialia into two Sub-orders, 
mainly distinguished from one another by the form and struc- 
ture of their teeth. It is true, indeed, that the more typical 
representatives of these two groups also differ from one another 
in regard to the structure of the hind foot; but there is one 
family which is intermediate in this respect, and thus shows 
how close is the relationship of the two groups. 
As already mentioned, the Marsupials have adapted them- 
selves to almost all modes of life, some running in the ordinary 
manner, some progressing on the ground by long leaps, others 
being arboreal, and others volant, after the manner of the 
Flying Squirrels, while a single species has taken to a subter- 
ranean Mole-like life. It is, however, very remarkable that not 
a single Australian representative of the Order is aquatic in its 
habits, so that such an animal as a “‘ Marsupial-Otter ” does not 
exist in that region. The place in nature thus left vacant by the 
Marsupials has been seized upon by the Duck-bill and by two 
members of the Rodent order (otherwise so poorly represented 
in Australia), of which the best-known is commonly termed the 
Beaver-Rat (Hydromys chrysogaster). In South America one 
of the Opossums—the Water-Opossum—has, however, assumed 
aquatic habits, having webbed feet, and passing most of its 
time in the waters of rivers and streams. 
Except for their skins, some of which are imported in large 
numbers to Europe, where they have a considerable value, the 
Marsupials are of little commercial importance toman. None 
of the herbivorous species have been domesticated as a source 
of food-supply, their flesh being apparently but seldom eaten 
at all; while all the larger carnivorous kinds are killed off as 
pests whenever met with, one or two having indeed been well- 
nigh exterminated in many districts. 
