chap, ii.] THE ELEMENTARY FACTS OF DISTRIBUTION. 13. 
established between an animal and its native country, and a 
new set of problems at once sprang into existence. From the- 
old point of view the diversities of animal life in the separate 
continents, even where physical conditions were almost identical, 
was the fact that excited astonishment ; but seen by the light 
of the evolution theory, it is the resemblances rather than the 
diversities in these distant continents and islands that are most 
difficult to explain. It thus comes to be admitted that a know- 
ledge of the exact area occupied by a species or a group is 
a real portion of its natural history, of as much importance 
as its habits, its structure, or its affinities ; and that we can 
never arrive at any trustworthy conclusions as to how the present 
state of the organic world was brought about, until we have 
ascertained with some accuracy the general laws of the dis- 
tribution of living things over the earth’s surface. 
Areas of Distribution . — Every species of animal has a certain 
area of distribution to which, as a rule, it is permanently 
confined, although, no doubt, the limits of its range fluctuate 
somewhat from year to year, and in some exceptional cases may 
be considerably altered in a few years or centuries. Each 
species is moreover usually limited to one continuous area, 
over the whole of which it is more or less frequently to be met 
with, but there are many partial exceptions to this rule. Some 
animals are so adapted to certain kinds of country — as to forests 
or marshes, mountains or deserts — that they cannot live long 
elsewhere. These may be found scattered over a wide area in 
suitable spots only, but can hardly on that account be said to 
have several distinct areas of distribution. As an example we 
may name the chamois, which lives only on high mountains, 
but is found in the Pyrenees, the Alps, the Carpathians, in 
some of the Greek mountains and the Caucasus. The variable 
hare is another and more remarkable case, being found all over 
Northern Europe and Asia beyond lat. 55°, and also in Scotland 
and Ireland. In Central Europe it is unknown till we come to 
the Alps, the Pyrenees, and the Caucasus, where it again appears. 
This is one of the best cases known of the discontinuous dis- 
tribution of a species , there being a gap of about a thousand miles 
between its southern limits in Russia, and its reappearance in 
