CHAP. II THE ELEMENTARY FACTS OF DISTRIBUTION 13 



forms closely allied to it already lived, a real and important 

 relation was 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 knowledge 

 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 pre- 

 sent state of the organic world was brought about, until we 

 have ascertained with some accuracy the general laws of 

 the distribution 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 per- 

 manently 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 

 apparent and some real 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, 

 permanently, live elsewhere. These maybe 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 dis- 



