BLAKISTON was the first who studied scientifically the distribution of mammals and birds in Hokkaido and in north-eastern part of the Main Land. He insisted from the zoological point of view that Hokkaido was once a part of Asiatic Continent. According to him Tsugaru Strait is an important line of demarcation of animal distribution in northern Japan (BLAKISTON, 1883). However, HATTA (1913) did not agree with BLAKISTON when he investigated Reptilian and Amphibian fauna of Sakhalin comparing with those of Hokkaido. For example the snake of Sakhalin is Vipera berus which occurs in northern part of Eurasian Contient while the snakes of Hokkaido are those which are very common in the Main Land. Therefore, he pointed that Soya Strait between Sakhalin and Hokkaido is zoogeographically more important than Tsugaru Strait.
There has been a confusion concerning the origin of animals in northern Japan. Recently Salamandrella keyserlingii which is a continental salamander has been found in Hokkaido. The pika and continental lizard, Lacerta vivipara have been also captured in Hokkaido. From this HATTA's opinion seems to be denied. BLAKISTON did not mentioned why the deer and the raccoon dog which are inhabitants of the Main Land are found in Hokkaido.
Recently paleontological as well as geological studies of Japan has been much advanced and it has been ascertained that in ancient glacial period either Soya Strait or Tsugaru Strait disappeared as a result of the lowering down of the sea level. Either BLAKISTON's theory or Hatta's opinion is recognizable when we take into account ancient geological changes of northern Japan.
However, we shall pay attention to the migration of animals by means of drift ice which has sometimes brought the fox from Kurile to Hokkaido.
