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

chap, x.] THE PAL^EARCTIC REGION 231usual dividing line of the Palsearctic and Oriental regions. Thecauses of such a phenomenon are not difficult to conceive. Evennow, that portion of the Palsearctic region between WesternAsia and Japan is, for the most part, a bleak and inhospitableregion, abounding in desert plateaus, and with a rigorous climateeven in its most favoured districts, and can, therefore, supportbut a scanty population of snakes, and of such groups ofinsects as require flowers, forests, or a considerable period ofwarm summer weather ; and it is precisely these which arerepresented in Japan and North China by tropical forms.Wemust also consider, that during the Glacial epoch this wholeregion would have become stillless productive, and that, as thesouthern limit of the ice retired northward, it would be followedup by many tropical forms along with such as had been drivensouth by its advance, and had survived to return to theirnorthern homes.It isalso evident that Japan has a more equable and probablymoister climate than the opposite shores of China, and has alsoa very different geological character, being rocky and broken,often volcanic, and supporting a rich,varied, and peculiar vegetation.It would thus be well adapted to support all the morehardy denizens of the tropics which might at various timesreach it, while it might not be so well adapted for the moreboreal forms from Mongolia or Siberia. The fact that a mixtureof such forms occurs there, is then, little to be wondered at, butwe may rather marvel that they are not more predominant, andthat even in the extreme south, the most abundant forms ofmammal, bird, and insect, are modifications of familiar Palaearctictypes. The fact clearly indicates that the former land connectionsof Japan with the continent have been in a northerlyrather than in a southerly direction, and that the tropical immigrantshave had difficulties to contend with, and have found theland already fairly stocked with northern aborigines inevery class and order of animals.almostGeneral Conclusions as to the Fauna of the Palccarctic Region.—Fromthe account that has now been given of the fauna