8 DR. BLANFORD’S REALMS CHAP. 
4 
can be traced, it results as a conclusion that from a given area of 
origin the group in question migrated in all directions where 
possible to a varying degree; it then died out in intervening 
tracts, or was left only in a certain part of its former and more 
extensive area of range. 
Zoological Regions.—Seeing that each species of animal has 
its own definite range, it is clear that the earth’s surface can be 
apportioned into divisions which are characterised by their 
animal inhabitants. We shall divide the earth into realms, 
which are the largest divisions; then into regions; and 
finally into subregions. It must be borne in mind that the 
various groups of the animal kingdom are of different ages, 
geologically speaking, and have therefore had less or more time, 
as the case may be, to settle down into their present distribution, 
and that different animals differ greatly in their rate of multi- 
plication, their power of migration, and their susceptibility 
to the effectiveness of various natural and other barriers to 
distribution. It is not, therefore, possible to divide the 
world into realms and regions which shall express the facts of 
distribution of the entire animal kingdom. Such divisions, 
which are common in text-books of zoology having but a small 
section devoted to zoogeography, are at best mere approximations 
and averages; no good is gained by taking such a comprehen- 
sive view of the matter, as the essential object of subdividing 
the earth’s surface is thereby lost sight of. The zoogeographical 
division of the earth which will be adopted here is that origin- 
ally recommended by Dr. Blanford, and now accepted by a 
number of authorities. There are three “realms,” to which a 
fourth may perhaps be added—though on negative grounds, and 
merely for the purpose of emphasising the parts of the world to 
which mammals have not gained access. The realms are again 
divisible into regions, at least in the case of one of them, and 
the regions may be again separated into more or less distinct 
subregions or provinces. The three primary divisions or realms 
which contain mammals are the Notogaean, including Australia 
and certain islands to the north of it; the Neogaean, or the 
South American continent and Central America; the Arcto- 
gaean, including the continents of North America, Europe, Asia, 
and Africa, together with the adjacent islands, such as the 
West Indies, East Indies (exclusive of those which fall within 
