t 



in Zoological and Botanical Geography. 5 



plain the discrepancies already mentioned. And, first, bow 

 is it that the snakes in Japan are Indian and the batrachians 

 Palaearctic ? Dr Gunther informs us, in the paper already 

 alluded to, that snakes are a pre-eminently tropical group, 

 decreasing rapidly in the temperate regions, and absolutely 

 ceasing at 62" N. Lat. Bactrachians, on the other hand, are 

 almost as fully developed in northern as in tropical regions. 

 They can support intense cold, and are, moreover, more dif- 

 fusible, geographically, than snakes. These facts furnish a 

 clue to the peculiarities of the Japanese reptile fauna. For 

 let us suppose that Japan once formed a part of northern Asia 

 (with which it is even now almost connected by two chains 

 of islands), it would then have received its birds, mammals, 

 and batrachians from the Palaearctic region ; but there could 

 have been few or no snakes, owing to the much lower curve 

 of the isothermal lines in Eastern Asia than Western Europe, 

 giving to Mandtchouria a climate as rigorous as that of 

 Sweden. Now, at a subsequent period, Japan must have 

 been connected with Southern Asia through the line of the 

 Loo-choo and Madjicosima islands, and would then acquire 

 its population of Indian forms of snakes, which would easily 

 establish themselves in an unoccupied region, — whereas the 

 batrachians, as well as the birds and mammals of Southern 

 Asia, would find a firmly established Palsearctic population 

 ready to resist the invasion of intruders, and it is therefore 

 not to be wondered at that but few, if any, Indian forms of 

 these groups should have been able to maintain themselves. 

 Again, the insects of Japan are decidedly Palsearctic in 

 character, except in the case of a few tropical forms of 

 diurnal lepidoptera, which would have been able to establish 

 themselves, like the snakes, on account of the extreme 

 poverty of that group in high latitudes. It would thus 

 appear that the tropical character of the snakes is quite ex- 

 ceptional, depending upon the fact of the whole group being 

 pre-eminently tropical, and can therefore not be held to 

 throw any doubt on the position of Japan in the Palsearctic 

 zoological region. 



We have next to consider the supposed discrepancy in the 

 mammals of Algeria compared with the birds, reptiles, 

 insects, and plants — all of which are decidedly of PalEearctic 



