189 



which they are adjusted to the peculiarities of the region 

 in which they obtain, that they are strictly an esoteric 

 assemblage, inhabiting the actual sites (or nearly so) of 

 their original debut upon this earth. Here, then, we 

 have a sufficient length of time for developments to have 

 taken place; they are all exposed to the self-same 

 agencies from without (for they live principally in com- 

 munion) yet, though I have examined carefully more 

 than a thousand specimens (a large proportion of them 

 beneath the microscope), I have never discovered a 

 single intermediate link which could be regarded as in a 

 transition state between any of the remainder. But 

 how is this ? Is it possible to account for differences so 

 decided, yet each of such amazing constancy, amongst 

 the several creatures of a central type which have been 

 exposed to identical conditions through, at any rate, 

 generations innumerable? They clearly cannot be ex- 

 plained on the doctrine of transmutation : yet they are 

 no exceptions to the ordinary rule, occupying an ana- 

 logous position to the members of every other endemic 

 group. 



But I will not occupy more space on the transmuta- 

 tion theory : suffice it to have shown that, in thus con- 

 ceding a legitimate power of self-adaptation, in accord- 

 ance with external circumstances, to the members of the 

 insect world; and in suggesting the inquiry, whether 

 the action of physical influences has been adequately 

 allowed for by entomologists generally (or, in other 

 words, whether the small shades of difference which 



