194 HISTORY OF THE EUROPEAN FAUNA. 



ranging southward as far as Persia and parts of 

 Asia Minor. Crossing the European border, we 

 find it in Russia, Upper Hungary, North and Central 

 Germany, being rarer in the south, Denmark, and 

 Scandinavia. According to Bedriaga, it crosses the 

 Rhine only in Alsace, but occurs no farther west. It 

 only just enters Holland. If we suppose the species 

 to have originated in Central Europe, we should 

 expect to find it in Switzerland, France, and perhaps 

 England. If it had its ancestral home in Eastern 

 Europe, we might expect it to occur on the Balkan 

 peninsula. It seems to me more probable, therefore, 

 that Rana arvalis came with the Siberian migration. 

 This need not cause surprise, as the genus Rana is 

 certainly not European. Out of about no species, 

 only four are peculiar to Europe, the rest are scattered 

 over all parts of the globe. Moreover, the fact that 

 these four species are confined to Southern Europe 

 would seem to indicate that the first species entered 

 from the south, and there either became modified or 

 spread over nearly the whole continent, as did, for 

 instance, Rana esculenta and R. temporaries Neither 

 of these is by any means confined to Europe. R. 

 esculenta ranges right across the Asiatic continent to 

 Japan, and also enters North Africa, while the other 

 has a wide distribution in northern and temperate 

 Asia. 



The various groups of Vertebrates are not dependent 

 on each other in their migrations. Mammals and Birds 

 extend their range with so much greater facility than 



