ORIGIN, ETC., OF THE EUROPEAN RHOPALOCERA. 249 



derived from Siberia. If this was the case, and it seems very 

 likely to be correct, the majority of them probably immigrated 

 westwards at the commencement of the pleistocene period, for 

 they must be of great antiquity ; moreover, it is unreasonable to 

 suppose that many of the species could not have existed also in 

 the South of Europe, even at the climax of the glacial epoch. 

 According to the same authority, only eight species have been 

 derived from Africa and thirty-nine from Asia, south of Siberia ; 

 that is, the oriental region of Prof. Wallace. These must in all 

 cases have immigrated into tbe south European province of the 

 palaearctic region after the termination of the glacial period, as 

 they belong to genera and types of tropical distribution. At tbe 

 present day they occur in those countries bordering on the Medi- 

 terranean Sea. 



The glacial species of butterflies — that is, the most ancient 

 forms, designated by Prof. August Weismann, " the original 

 stirps" — are in many cases distinguished by their melanic and 

 melanochroic tendencies. We thus find the forms inhabiting the 

 more northern localities and higher elevations on the mountains 

 often of a darker hue, while their representatives in more 

 southern latitudes and less elevated altitudes exhibit a brighter 

 coloration. The researches of the learned German above named 

 confirm this view, although in a few instances the reverse seems 

 to be the case, the more austral forms exhibiting melanistic ten- 

 dencies, while their representatives in boreal localities possess 

 either a brighter or a more pallid coloration. 



Without entering here into the discussion as to whether these 

 melanic forms have been produced by the direct or indirect action 

 of the local conditions, I think I may safely assert my belief that 

 those belonging to the austral group owe their evolution to post- 

 glacial times, and are consequently of much more recent origin. 



The comparative paucity of the European rhopalocerous 

 fauna is to be accounted for in two different ways. The first is 

 that insufficient time has elapsed since the termination of the 

 glacial period to permit of the appearance of many new species 

 to replace those which were extirpated by the great cold. At 

 about the climax of the glacial period, as Prof. James Geikie 

 informs us, the land connection between Europe and Africa was 

 severed, which resulted in the entire extinction of many species 

 of a more austral character which were driven south, and survived 

 for a time in the area which the Mediterranean now occupies. 

 The second one consists in the great and insurmountable barriers 

 to the immigration of austral forms, furnished by the elevated 

 chain of the Himalayas and the vast sandy tract of the Sahara ; 

 otherwise, were these not existing, many oriental and ethiopian 

 butterflies would no doubt extend the area of their distribution 

 to the north, where they could easily find a congenial home on 

 the shores of the Mediterranean. 



