The geographical distribution of animals, with a study of the relations ...

58 DISTRIBUTION OF ANIMALS. [part i.maintained. For they will find, that a careful consideration ofthe exceptional means of dispersal and conditions of existence ofeach group, will explain most of the divergences from the normaldistribution of higher animals.We shall thus be led to an intelligent comprehension of thephenomena of distribution in all groups, which would not bethe case if every specialist formed regions for his own particularstudy. In many cases we should find that no satisfactorydivision of the earth could be made tocorrespond with the distributioneven of an entire class ; but we should have the coleopteristand the lepidopterist each with his own Geography.Andeven this would probably not suffice, for it is very doubtful ifthe detailed distribution of the Longicornes, so closely dependenton woody vegetation, could be made to agree with that of theStaphylinidse or the Carabidse which abound in many of themost barren regions, or with that of the Scarabeidse, largely dependenton the presence of herbivorous mammalia.And wheneach of these enquirers had settled a division of the earth into" regions "which exhibited with tolerable accuracy the phenomenaof distribution of his own group, we should have gainednothing whatever but a very complex mode of exhibitingthe bare facts of distribution. We should then have to beginto work out the causes of the divergence of one group fromanother in this respect ; but as each worker would refer to hisown set of regions as the type, the whole subject would becomeinvolved in inextricable confusion. These considerations seemto make it imperative that one set of "regions" should beestablished as typical for Zoology ; and it is hoped the reasonshere advanced will satisfy most naturalists that these regionscan be best determined, in the first place, by a study of the distributionof the mammalia, supplemented in doubtful cases bythat of the other vertebrates.We will now proceed to a discussionof what these regions are.Various Zoological Regions proposed since 1857.— It has alreadybeen pointed out that a very large number of birds are limitedby the same kind of barriers as mammalia ;it will thereforenot be surprising that a system of regions formed to suit the