THE AMERICAN NATURALIST. [Vol. XXXVII. 



lidae. Some of these have a much more extended range in this con- 

 tinent than in the Old World. I'm r hippo/iica for example being found 

 as an European species only in the extreme north, while with us it 

 reaches south as far as Texas. This adaptability is a potent factor 

 in distribution and the readiness with which a given species assimi- 

 lates with new surroundings has a powerful bearing upon its final 

 geographical range. Insects coming to us from Asia by the path 

 mentioned may spread to the south through the great valleys lying 

 between the Rocky Mountains and the Cascades or by use of the 

 passes in the former range gain the great plains of Canada and 

 eventually appear on the Atlantic coast. If their nature is such as 

 to enable them to bear an arid or warm climate they may reach 

 points far to the south since there are no great natural barriers in 

 the way. 



The southwestern gateway is, in Professor Webster's opinion, by 



of a fauna received through this medium he cites Halisidota, a genus 

 of moths apparently South American in type. Some of our forms 

 are supposed to have had their origin in the South and to have come 



range from Argentina to Costa Rica is thought to be the stem of our 

 H. tesselaris and H. citripcs, which seem to have reached us by two 

 different courses— the one coming north by way of Texas, the 

 other east by way of Yucatan and Cuba. The distribution of Pacific 

 and northern Halisidota- indicate to the author the probability of 

 certain species having reached (through stem forms) the New Eng- 

 land coast by following the Pacific Maritime trend from Central 

 America through California, Oregon, Washington and British 

 Columbia, thence traveling eastward along the lines indicated for 

 the immigrants of Asiatic origin. The genus Diabrotica, among the 

 beetles, warrants the belief that offshoots of a common Central 

 American stem may become separated far to the south, one going to 

 the Pacific district while its fellow inhabits the Atlantic slope. 



But little matter concerning the antillean trend is presented, this 

 being thought of less importance than the others, though many 

 insects appear to have come in that way. 



Concerning the route taken by insects introduced through the 

 eastern ports by agency of man, Professor Webster has ascertained 

 that they follow a path which he calls the transappalachian trend — 

 reaching the fertile prairies of the interior through the great gap in 

 New York which forms the principal thoroughfare for insect invasion. 



