160 THE ENTOMOLOGIST. 



I have given elsewhere (Entom, xxix. 3*20-324) my reasons for 

 supposing that the alpine Pihopalocera fauna did not retreat as 

 far south as the north of Europe during the glacial period. That 

 the climatal conditions were not so severe as supposed hy Hof- 

 mann in order to have extirpated tlie whole of the Rhopalocera 

 fauna of Europe is proved by the paucity of alpine forms which 

 are found on the various mountain ranges in the extreme south 

 of the Continent at the present day. The same thing must 

 have been the case in the other portion of the Palaarctic Area, 

 judging from the fact that there are so few species found on the 

 Himalayas and the mountains of Northern Persia to the south. 



All these facts seem to prove that the great majority of the 

 alpine forms of butterflies therefore found a sanctuary during 

 the climax of the glacial period to the immediate south of the 

 three great chains of mountains on either continent. 



Hofmann is most probably correct in concluding that the 

 great bulk of the European Pihopalocera fauna have been 

 originally derived from the Asiatic Area, though not, as he sup- 

 poses, after the termination of the glacial epoch ; but I think he 

 is incorrect in imagining that the post-glacial alpine forms were 

 not directly derived from the south. According to the investi- 

 gations of Sir Joseph Hooker, the alpine flora of the Himalayas, 

 the Alps, and Pyrenees have had remarkably little lateral con- 

 nection with each other in post-glacial times. It is reasonable 

 to suppose therefore that the alpine PJiopalocera have accord- 

 ingly not been directly derived from the East in a similar man- 

 ner. The butterflies being so dependent upon the plants for 

 their pabula must have been in large measure circumscribed by 

 their migration. On the other hand, it may be probably true 

 that the great majority of the Austral or Lowland forms immi- 

 grated westwards from Asia at the termination of the glacial 

 epoch. 



In the case of the Nearctic Continent, fully taking into con- 

 sideration the more extreme glaciated conditions which pre- 

 vailed there, I think the alpine butterflies were not driven any 

 further south than the latitude of 30'^ N. ; but there are so few 

 alpine forms occurring in that region that it would not be safe to 

 draw the line so closely as one is able to do in the Eastern 

 Hemisphere. Moreover, the physical conditions of the two 

 regions are very difterent, the elevated chain of the Cordilleras 

 running at right angles to and crossing the equator, while all the 

 principal mountain ranges of the Palaearctic Eegion are in the 

 reverse direction, that is, nearly parallel with the equatorial belt. 

 The fact that closely allied genera to that of Erdna occur in the 

 Andes of South America, and again in the highlands of South 

 Africa, may be explained on the hypotheses that they were 

 derived from the regions to the north during the glacial epoch ; 

 in the former case by means of the elevated chain of the Cor- 



