Home, and Range East of Mountains. 63 



not generally easy to say precisely what they are. Assum- 

 ing that I have correctly placed the native home of the spe- 

 cies in the higher, treeless and scarcely habitable plains of 

 the Rocky Mountain region of the Northwest, and that it 

 is sub-alpine, we may perhaps find, in addition to the com- 

 paratively sudden change from an attenuated and dry to 

 a more dense and humid atmosphere, another tangible 

 barrier to its permanent multiplication in the more fertile 

 country to the southeast, in the lengthened summer season. 

 As with annual plants, so with insects (like this locust) 

 which produce but one generation annually and whose 

 active existence is bounded by the spring and autumn 

 frosts — the duration of active life is proportioned to the 

 length of the growing season. Hatching late and develop- 

 ing quickly in its native haunts, our Rocky Mountain 

 Locust when born within our borders (and the same 

 will apply in degree to all the country where it is not 

 autochthonous), is in the condition of an annual north- 

 ern plant sown in more southern climes ; and just as this 

 attains precocious maturity and deteriorates for want of 

 autumn's ripening influences, so our locust must in such 

 circumstances deteriorate. If those which acquired wings 

 in Missouri, Kansas, Iowa, etc., early in June of 1875, had 

 staid long enough to lay eggs, supposing them capable of 

 doing so, these eggs would inevitably have hatched prema- 

 turely, and the progeny must in consequence have perished. 

 There would have been no time for a second generation to 

 mature: such a second generation would have been cut off 

 by winter's frosts without perpetuating. 



Being a firm believer in change by modification in what 

 we call species, and that climatic conditions play a most 

 important part in causing this change, and that they act 

 more rapidly with lower animals than most evolutionists 

 grant, the idea has been very strong in my mind that the 



