74 THE CLASS OF INSECTS. 



"The western district is the maritime slope of the continent 

 to tlie Pacific, and thus inchides Califoinia. Oregon, and Wash- 

 ington Territories. 



"Tliese gi-eat districts are divided into a number of prov- 

 inces, of unequal size, and which are limited by changes in 

 climate, and therefore sometimes distincth', sometimes vagueh^ 

 defined." 



"The method of distribution of species in the Atlantic and 

 Pacific districts, as already observed by me in various memoirs, 

 is entire!}' different. In the Atlantic district, a large number 

 of species are distributed over a large extent of country ; man^- 

 species are of rare occurrence, and in passing over a distance 

 of several hundred iniles, but small variation will be found in 

 the species obtained. In the Pacific district, a small number 

 of species are confined to a small region of country ; most 

 species occur in considerable numbers, and in travelling even 

 one hundred miles, it is found that the most abundant species 

 are replaced by others, in man}' instances verj' similar to them ; 

 these small centres of distribution can be limited onl}' after 

 careful collections have been made at a great number of locali- 

 ties, and it is to be hoped that this very interesting and im- 

 portant subject of investigation maj- soon receive proper atten- 

 tion from the lovers of science of our Pacific shores. 



"In the Central district, consisting, as it does to a ver}'- 

 large extent, of deserts, the distribution seems to be of a mod- 

 erate number of species over a large extent of countrj-, with a 

 considerable admixture of local species ; such at least seems to 

 be the result of observations in Kansas, Upper Texas, and 

 Arizona." 



There are a ver}' few species which range from Xew England 

 to Brazil, and fewer still (Xyleutes robinio', according to Bois- 

 duval, is found in California) range from New England to 

 California. Junonia coeiiia, according to authors, is found both 

 in the Southern States and California, and P>/n-harctia isaheUa 

 of the Eastern States would be easil}' confounded with P. Cali- 

 fornica. 



Variation. Islands afford more variable forms than conti- 

 nents ; the Madeiran insects and those of Great Britain varj^ 

 more than the same species found on the continent of Europe. 



