﻿OP IHB STATE ENTOMOLOGIST. 113 



THE CONDITIOXS WHICH PKEVEXT THE PERMANENT SETTLEMENT OF THE SPECIES 



IN MISSOURI. 



The conditions which determine the geographical limits in which 

 a species can exist, are often complex, and it is not generally easy to 

 say precisely what they are. Assuming that I have correctly placed 

 the native home of the species in the higher, treeless and uninhabita- 

 ble plains of the Rocky Mountain region of the northwest, and that it 

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

 den 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 Sum- 

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

 which produce but one generation annually and whose active exis- 

 tence is bounded by the Spring and Autumn frosts — the duration of 

 active life is proportioned to the length of the growing season. Hatch- 

 ing late and developing quickly in its native haunts, our Rocky Moun- 

 tain Locust when born within our borders (and the same will apply in 

 degree to all the country where it is not autochtonous), is in the con- 

 dition of an annual northern 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 deteriorate 

 under such circumstances. If those which acquired wings in Missouri 

 early last June had staid with us long enough to lay eggs, even sup- 

 posing them capable of doing so, these eggs would have inevitably 

 hatched prematurely and the progeny must in consequence have per- 

 ished. 



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 than most evolu- 

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

 species might become profoundly modified in the direction oi Atlanis 

 in the course of two or three generations in the country to the south- 

 east, and that in this way and through miscegenation with our native 

 species, its extinction from our territory might also be accounted for. 

 It has also been suggested by Prof.Thomas — a professed anti-Darwinian 

 — in an elaborate paper published last October in the Chicago //i^Jer- 

 Ocean^ and, as bearing on this point, I will state that the specimens 

 which hatched- in and left our western counties last Spring were, on 

 an average, somewhat darker and smaller than their parents. But 

 afterfully digesting all the facts, I am convinced that these influences 

 play a very unimportant part, if any ; and that they cannot be con- 

 sidered as factors in the problem. All that could get away from the 

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