332 



LIFE, IN ITS HiGHLR FORMS. 



length the latter receives no more. It now dies for lack 

 of sustenance : shrivels, dries, and peels off 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 more 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 



