CHAP. II.] THE ELEMENTARY FACTS OF DISTRIBUTION. 



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established between an animal and its native country, and a 

 new set of problems at once sprang into existence. From tlie 

 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 mountams 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 Eussia, and its reappearance in 



