CHAP. X.] THE PAL^ARCTIC REGION. 231 



■usual dividing line of the Palsearctic and Oriental regions. The 

 causes of such a phenomenon are not difficult to conceive. Even 

 now, that portion of the Paltearctic region between Western 

 Asia and Japan is, for the most part, a bleak and inhospitable 

 region, abounding in desert plateaus, and with a rigorous climate 

 even in its most favoured districts, and can, therefore, support 

 but a scanty population of snakes, and of such groups of 

 insects as require flowers, forests, or a considerable period of 

 warm summer weather ; and it is precisely these which are 

 represented in Japan and North China by tropical forms. We 

 must also consider, that during the Glacial epoch this whole 

 region M'ould have become still less productive, and tliat, as the 

 southern limit of the ice retired northward, it would be followed 

 up by many tropical forms along with such as had been driven 

 south by its advance, and had survived to return to their 

 northern homes. 



It is also evident that Japan has a more equable and probably 

 moister climate than the opposite shores of China, and has also 

 a very different geological character, being rocky and broken, 

 often volcanic, and supporting a rich, varied, and peculiar vege- 

 tation. It would thus be well adapted to support all the more 

 hardy denizens of the tropics which might at various times 

 reach it, while it might not be so well adapted for the more 

 boreal forms from Mongolia or Siberia. The fact that a mixture 

 of such forms occurs there, is then, little to be wondered at, but 

 we may rather marvel that they are not more predominant, and 

 that even in the extreme south, the most abundant forms of 

 mammal, bird, and insect, are modifications of familiar Pahcarctic 

 types. The fact clearly indicates that the former land con- 

 nections of Japan with the continent have been in a northerly 

 rather than in a southerly direction, and that the tropical immi- 

 grants have had difficulties to contend with, and have found the 

 land already fairly stocked with northern aborigines in almost 

 every class and order of animals. 



General Conclusions as to the Fauna of the Valmarctic Re- 

 gion. — Prom the account that has now been given of the fauna 



