.332 
LIFE, IN ITS HIGHER FORMS. 
length the latter receives no more. It now dies for lack 
of sustenance : shrivels, dries, and peels oil’ in shreds, or 
is rubbed off by the animal against the trees and palings. 
The horns are now no longer sensitive, but can be used as 
effective weapons of offence. After a time, however, the 
thick ring of bone begins to be absorbed, particle by 
particle, and the absorptive process goes on until a com- 
plete separation of the horn is effected, which then falls off 
by its own weight from the basal prominence. The 
latter is presently covered with skin, and awaits the 
return of spring to bud anew. 
The geographical distribution of animals is a subject of 
great interest to the naturalist; that is, the manner in 
which we find particular species either spread over con- 
siderable portions of the world, confined to small tracts of 
country, or appearing in remote but isolated regions. No 
country affords moro interesting phenomena connected with 
this subject than the continent of Australia with its cir- 
cumjacent islands. Excluding the Seals and Whales of its 
coasts, the Mammalia known to inhabit this great region 
as large as Europe — amount to about a hundred and twenty 
species, the whole of which are absolutely confined to it. 
Of these about a hundred are marked by some remarkable 
peculiarities of structure, which have induced zoologists to 
separate them from all other Mammalia, forming them 
into a Sub- class by themselves, under the name of Mar- 
supialia. In order to appreciate the importance of these 
facts, we must look at the part which this Sub-class plays 
in the zoology of other parts of the world. The total 
