GEOGRAPHICAL DISTRIBUTION 



commonly called Polynesia, avoiding, however, the northern outliei'S 

 of the New-Zealand Region, and so return to encompass Australia 

 proper and Tasmania. 



Though the characteristic Mammals of the Australian Region 

 are highly remarkable, comprehending as they do the whole of the 

 most peculiar {Ornithodelphia) of the three Subclasses and nearly all 

 of a second {Didclphia), by far the largest portion of the area it covers 

 is weak if not wanting in Mammalian life, and its zoological features 

 are nearly as well exhibited by its Birds. Nor can mention be hei'e 

 omitted of the remarkable Ganoid Fish, Ceratodus, a genus which 

 has come down to us unaltered from Mesozoic times, — all facts 

 serving to shew that the isolation of Australia is probably the next 

 oldest in the world to that of New Zealand, having possibly 

 existed since the time when no Mammals higher than Marsupials 

 had appeared on the face of the earth. ^ 



The prevalent zoological features of any Region are of two kinds 

 —negative and positive. It is therefore just as much the business 

 of the zoogeographer to ascertain what groups of animals are wanting 

 in any particular locality (altogether independently of its extent) as 

 to determine those which are forthcoming there. Of course, in 

 the former case, it would be idle to regard as a valuable physical 

 feature of a district the absence of groups which do not occur except 

 in its immediate neighbourhood ; but when we find that certain 

 groups, though abounding in some part of the vicinity, either 

 suddenly cease from appearing or appear only in very reduced 

 numbers, and occasionally in abnormal forms, the fact obviously has 

 an important bearing. Now, as has been above stated, mere 

 geographical considerations, taken from the situation and configrua- 

 tion of the islands of the Indian or Malay Archipelago, would 

 indicate that they extended in an unbroken series from the Strait of 

 Malacca to New Guinea, or even fui'ther to the eastward. Indeed, 

 the very name Australasia, often applied to this part of the world, 

 would induce the belief that all those countless islands were but a 

 southern prolongation of the mainland of Asia— broken up, it is true. 

 But so far from this being the case a very definite barrier is inter- 

 j)osed. A strait, some 15 or 20 miles wide, dividing, as just stated, 

 the two otherwise insignificant islands (Bali and Lombok), makes 

 such a frontier as can hardly be shewn to exist elsewhere. The 



former belongs to the Indian Region, the latter to the Australian, 

 and between them there is absolutely no true transition — that is, no 

 species are common to both which cannot be easily accounted for 

 by the various accidents and migrations that in the course of time 



^ It will be borne in nihid that fossil remains shew that Marsupials once in- 

 habited Europe. They are now restri'^ted to Australia with the exception of one 

 group, which inhabits the Neotropical Region, a single species ranging also over 

 the temperate parts of North America. 



