276 MICHIGAN SURVEY, 1908. 



In discussing the geographic origin of the butterflies common to- 

 the old and new worlds, Scudder seldom attempts more than a hemis- 

 pherical location. In discussing the origin of American faunae that 

 are both boreal and Asiatic, it is well to recall that geologically speak- 

 ing the American boreal and arctic are largely of recent origin in the 

 northern regioiis. It is therefore not unlikely that many of these forms 

 which it has been customary to consider boreal are in reality not so, 

 but from high altitudes — from the North American Cordilleras or from- 

 the Himalayas, where high altitude and low temperature existed long 

 before the Ice Age. With the development of an Ice Age, there was 

 a great increase of this low temperature, lowland habitat and whem 

 once the glacial climate declined a vast area was open for invasion — - 

 an area of such great extent that we have become thoroughly accustomed 

 to think the fauna has originated there. It has thus become customary 

 to speak of them as of northern origin, in spite of the fact that we kncwr 

 that they are almost entirely post-Glacial migrants from the south. 



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