200 HISTORY OF THE EUROPEAN FAUNA. 



mologists as a south-eastern form, seems to have 

 arrived with the Siberian migration, whilst the closely 

 allied D. atricapillus, which has been able to reach 

 Ireland, has a wider range and came earlier with the 

 Orientals. 



Messrs. Speyer state (p. 68) that almost all those 

 species of Central European Butterflies whose 

 northern limit is deflected southward as we approach 

 the west coast of Europe, inhabit also the Volga 

 country and the adjoining parts of Asia. Many of 

 them are much commoner there than in Central 

 Europe, and it appears probable to the authors of 

 the Geographical Distribution of Butterflies that 

 these species came from the east. Asia and Central 

 Europe have, according to Messrs. Speyer, no fewer 

 than 156 species in common. Mr. Petersen esti- 

 mates that no less than 91 per cent, of the Arctic- 

 European Butterflies also occur in Siberia. He 

 made a special study of the Arctic Macro-lepi- 

 doptera, and came to the conclusion that Central 

 Asia, not having been glaciated in the Ice-Age, 

 offered a possibility of existence to both animals 

 and plants. Here, he thinks, was the principal centre 

 to which Europe owed its re-population in post-glacial 

 times. Mr. Petersen is of opinion (p. 40) that the 

 Arctic-European Lepidoptera are composed of two 

 elements the pliocene relics which persisted in 

 Europe during the Glacial period, and the new 

 immigrants from Siberia. 



No doubt Siberia supplied Europe with a number 



