PRELIMINARY CONSIDERATIONS. 55 



The work published by Messrs. Speycr deals only 

 with the origin of the Central European Butterflies. 

 The period during which our European species 

 originated is not specified, but the authors believe 

 that they had their home either in Southern Russia 

 or Central Asia. The fact that the number of 

 butterflies decreases very considerably as we pro- 

 ceed north-westward in Europe appears to them 

 to substantiate these views. The apparent dislike 

 evinced by butterflies to the damp Atlantic Coast 

 climate, they think, clearly indicates that they had 

 originated in a dry and more continental climate. 

 The history of the North European Butterflies 

 and Moths has been carefully described by Mr. 

 Petersen. He adopts Hofman's theory as to the 

 almost total extinction of the Lepidoptera in 

 Europe during the Glacial period. The chief immi- 

 gration to Europe after that period is, he thinks, 

 Siberian. 



At first there appeared species which belonged 

 to a cold climate, and which now live in ele- 

 vated regions ; then came forms suited to a milder 

 climate, which established themselves on the north- 

 easterly slopes of the Alps. The most recent addition 

 which our continent has received from Siberia is, 

 according to Mr. Petersen, the present Scandinavian 

 fauna. Scandinavia has obtained a larger number of 

 species than the European plain, because to this last 

 migration were added such as prefer a northern or 

 Alpine climate. 



