98 GEOGRAPHICAL DISTRIBUTION. 



off into an almost uninhabitable desert. Along the coast-line, and 

 more especially on the eastern border, where vapour-condensing sur- 

 faces present themselves in the form of elevated mountain-crests, 

 there is an abundance of aqueous precipitation, to which a luxuri- 

 ous forest-growth responds. Less than one-half of the continent 

 lies within the tropics. Papua, which constitutes the second sub- 

 region, exhibits in great part a mountainous character, and, from 

 the abundance of aqueous precipitation distinctive of the equatorial 

 portions of the earth's surface, a vegetation of truly tropical luxuri- 

 ance. A dense forest growth likewise covers the greater portion 

 of New Zealand (third sub-region), where also we have the most 

 elevated mountain-summits in the region. 



Zoological Characters of the Australian Realm. The Aus- 

 tralian region is, by both positive and negative characters, the most 

 marked of any on the earth, and, indeed, so remarkable are its faunal 

 peculiarities that it has been thought by some to constitute properly 

 in itself a main zoogeographical division, as opposed to the rest of 

 the world. The most striking feature of this fauna is the general 

 absence, among the Mammalia, of such forms as, under favourable 

 conditions, are to be met with in all other portions of the earth's 

 surface. In the whole of this region all the terrestrial Mammalia 

 that are to be found in the Old World are absent, except a solitary 

 (possibly two) species of hog (Sus), found in New Guinea, the bats, 

 and rodents, the former being represented by about ten genera, 

 and the latter by the single family of the mice (Muridse). of which 

 the true mice (Mus) comprise more than one-third of all the vari- 

 ous forms. The edentates, insectivores, carnivores, and monkeys, 

 except such as have been introduced through the agency of man, 

 and possibly the " dingo," or Australian wild-dog, which may prove 

 to be indigenous, are wholly wanting, their place being filled by a 

 wonderful variety of the implacental mammals the marsupials and 

 monotremes the lowest of the entire mammalian series. No im- 

 placental mammals occur at the present time in any portion of the 

 Old World outside of the limits of the Australian and the connect- 

 ing Austro-Malaysian regions, and their only representatives in the 

 Western Hemisphere are the opossums (Didelphyidse), upwards of 

 twenty species of which range throughout the forest districts of the 

 Neotropical realm (with two species in North America). The Aus- 

 tralian marsupials fall into six distinct families : The Macropodidge, 



