THE SIBERIAN MIGRATION. 2OI 



of species of Butterflies and Moths in recent geo- 

 logical times, but we need not necessarily suppose 

 that these arrived only after the Glacial period. Even 

 the most extreme glacialists admit that large areas 

 on our continent were free from ice at the height of 

 the Ice-Age, Siberia had therefore no particular 

 advantage over Europe in giving an asylum to 

 Butterflies and Moths which were escaping from the 

 rigours of a supposed arctic climate. But we have 

 already learned (p. 80) that the climate during the 

 Glacial period probably differed but little from that 

 which we enjoy at the present day, and we may 

 assume, therefore, that the Lepidoptera of Siberia 

 migrated during that time or even earlier to 

 Europe. 



Let us for a moment reconsider some instances of 

 mammalian migration from Siberia, with a view to 

 studying more closely the nature of these great 

 events. I mentioned the fact that some of the 

 Siberian migrants have remained in England, that 

 more have settled down permanently on our con- 

 tinent, but that many others have either become 

 entirely extinct or do not live any longer in 

 Europe. 



Of the mammals which made their appearance in 

 Great Britain in recent geological times, t.e. y during 

 and since the deposition of the Forest-Bed for example, 

 the following species probably came direct from 

 Siberia across the plains of Europe, as already men- 

 tioned (p. 95): 



