CHAP. 1V.] 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 Palzarctic, 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 Palearctic 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 Palzearctic 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 
