THE SIBERIAN MIGRATION. IQ3 



interesting event actually took place. The Sand- 

 Lizard (Lacerta agilis\ another British species, may 

 be looked upon as an eastern form. It is quite absent 

 from Italy, the Balkan peninsula, and the Medi- 

 terranean Islands, but extends throughout Central 

 Europe to the east. 



Among the species of eastern Reptiles which have 

 a mere local range in Europe might be mentioned 

 the two Lizards, Phrynocephalus auritus and Agarna 

 sanguinolenta. They belong to the family Iguanidcs^ 

 which includes some very large species. Both of 

 them are Asiatic forms, which have only just pene- 

 trated across the eastern steppes into Europe, where 

 they inhabit the arid regions between the Caspian 

 and the River Don in Southern Russia. 



The species of Mammals living in Europe at the 

 present day have, with few exceptions, migrated 

 to our continent from other parts of the world. 

 With regard to the Birds, it is possible that a 

 somewhat larger number proportionally may be 

 of European origin. Still, the great majority are, 

 I think, to be regarded as immigrants. The autoch- 

 thones are about equal to the immigrant reptiles, 

 but many of the European Amphibians and the 

 majority of the Fishes have probably originated on 

 our continent. Some of the European Amphibia 

 especially among the tailless forms appear to be 

 immigrants from Asia. Thus the distribution of 

 Rana arvalis in Europe is remarkably like that of 

 a Siberian migrant. This frog occurs in Siberia, 



13 



