PEEFACE. 15 



separation, in this way, of local races or varieties 

 may have given rise to new species. There is first 

 to be considered the involuntary migrations of ani- 

 mals by being floated down rivers or conveyed by 

 the wind. As we study those which are provided 

 with wings, their voluntary migrations are seen to 

 play an important part in their life. Birds and 

 insects share these characters in common, riig-hts 

 of the Storm-Butterfly (Danaus Flex'qrpus) have 

 already been noticed crossing the Great Lakes in the 

 autumn, and going southward as if to endeavour 

 to hibernate in a warmer climate. This butterfly 

 hibernates in Alabama. Plights of butterflies have 

 been frequently observed in regions as remote as 

 the English Channel and the Amazon river. The 

 cotton-worm moth is strong-winged and has a lithe, 

 smoothly scaled body, offering very little resistance 

 to the wind. Although the wind may accelerate 

 and assist its migrations, I regard them as voluntary, 

 from the facts of its structure and the wide territory 

 which it covers. The cause of the northward mi- 

 gration of the cotton-worm moth from more south- 

 ern localities over the cotton belt, and as far north 

 as Canada, cannot be suggested as yet, the data not 

 being all known. One thing is clear, that the terri- 

 tory growing cotton, over which they pass, increases 

 their numbers by providing them with food, and 

 thus makes them an enemy of the cotton-planter. 



In the United States the yearly condition of the 

 crops has an immediate effect upon the general 

 prosperity of the country. Any thing affecting agri- 

 cultural interests thus becomes a matter of public 



