The Scottish Naturalist. 159 



North Europe and North America, which geologists suppose to 

 have once existed ; the other is across Behring's Straits or by 

 the Aleutian islands. As, however, these species of Anarta do 

 not occur in the eastern palsearctic region (/.<?., Siberia, &c.) nor 

 on the western side of North America, the route seems more 

 likely to have been by Greenland or polar lands north of it. It 

 is quite possible that the species originated in these polar lands, 

 and when driven southwards colonies were sent both to Europe 

 and America. 



Of the other species under discussion, the macro-lepidoptera 

 (the Erebia^ ZygcE?ia, Pachnobia, and Fsodos), all range pretty 

 widely, but, with the exception of Fsodos (a doubtful inhabitant 

 of Siberia), are confined to Europe. I expect that some of these 

 species may, hke many of the arctic-alpine plants, inhabit the 

 Himalaya, or even some of the African and other mountains, but 

 I have not been able to find any evidence of this. These species 

 may be as ancient as the Anartce, or they may not. Their 

 absence from America is slightly suggestive of the latter. 



Some of the micro-lepidoptera in question are also likely to 

 be of ancient origin ; but some of them may be, if they are con- 

 fined to Britain — a fact possible, but not probable — of compara- 

 tively recent evolution. 



In conclusion, the facts and suggestions put forward in this 

 paper may be thus summed up : — 



1. The British isles being at one time subject to extreme arctic 

 conditions, had no fauna or flora. 



2. At the close of the last glacial period they were peopled 

 by plants and animals from continental Europe. 



3. Most of these plants and animals reached Britain across 

 the dry or nearly dry bed of the German Ocean. 



4. Plants necessarily arrived before animals; and of the former, 

 certain classes of cryptogamic plants, and the maritime and wind- 

 fertilised species of the liigher plants, were the first comers. 



5. The arctic and arctic-alpine plants and animals, being 

 those that followed closest on the retreating ice, were amongst 

 the earliest arrivals, and had a wide range through the country. 



6. From their present distribution in Britain it is probable 

 that all the species (in question) did not enter Britain at the 

 parts nearest continental Europe, but that they reached it at 

 various points on the present east coast. 



7. The distribution of the species (treated of in this paper) 

 is not co-extensive with that of their food-plants. 



