chap. iv.] ZOOLOGICAL REGIONS. 65 



We see, then, that even the exceedingly rich and isolated Neo- 

 tropical region is less rich and diversified in its forms of mam- 

 malian life than the very much smaller area of the Indian region, 

 or the temperate Palcearctic, and very much less so than the 

 Ethiopian region ; while even the comparatively poor Nearctic 

 region, is nearly equal to it in the number of its family types. If 

 these were united they would possess fifty-five families, a number 

 very disproportionate to those of the remaining two. Another 

 consideration is, that although the absence of certain forms of 

 life makes a region more isolated, it does not make it zoologically 

 more important ; for we have only to suppose some five or six 

 families, now common to both, to become extinct either in the 

 Ethiopian or the Indian regions, and they would become as 

 strongly differentiated from all other regions as South America, 

 while still remaining as rich in family types. In birds exactly the 

 same phenomenon recurs, the family types being less numerous in 

 South America than in either of the other tropical regions of the 

 earth, but a larger proportion of them are restricted to it. It will 

 be shown further on, that the Ethiopian and Indian, (or, as I pro- 

 pose to call it in this work, Oriental) regions, are sufficiently differ- 

 entiated by very important groups of animals peculiar to each ; 

 and that, on strict zoological principles they are entitled to 

 rank as regions of equal value with the Neotropical and Aus- 

 tralian. It is perhaps less clear whether the Palsearctic should 

 be separated from the Oriental region, with which it has un- 

 doubtedly much in common ; but there are many and powerful 

 reasons for keeping it distinct. There is an unmistakably different 

 facies in the animal forms of the two regions ; and although no 

 families of mammalia or birds, and not many genera, are wholly 

 confined to the Palsearctic region, a very considerable number 

 of both have their metropolis in it, and are very richly represented. 

 The distinction between the characteristic forms of life in tropical 

 and cold countries is, on the whole, very strongly marked in the 

 northern hemisphere ; and to refuse to recognise this in a sub- 

 division of the earth which is established for the very purpose of 

 expressing such contrasts more clearly and concisely than by 

 ordinary geographical terminology, would be both illogical and 



