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There are currents of air in the heavens and currents of water in both 

 the oceans and inland streams, and all these have their iniiuence on in- 

 sect distribution. The influences of the Gulf stream of the Atlantic are 

 far reaching in their effects, as will be further explained, while the cor- 

 responding current, sweeping northward along the coast of eastern Asia 

 and south along the west coast of North America, is at present less im- 

 portant in its effects, owing largely, perhaps, to the Rocky Mountains and 

 the Great American Desert. There also seem to be currents of insect 

 migration. These, three in number, may be designated as follows : The 



Map milica mg, approximately, the natural divide between the northern and southern 

 insect faunas, east of the Kocky Mountains. 



Pacific coast, Northwestern and Southwestern. With the first we at pres- 

 ent have little to do, as owing, possibly, to the combined influences of the 

 mountains and desert intervening between us and the area directly in- 

 fluenced by it, we see little of the insect fauna of the Pacific coast. To the 

 influence of the Rocky Mountains I attribute the extension of Alaskan 

 forms southward to New Mexico. "Whether, with the barriers withdrawn, 

 these trans Pacific and sub-arctic species would drift eastward, is a problem 

 which will likely only be solved when some gigantic system of irrigation 



