124 THE entomologist's RECOKI). 



they rest ; but even here, in the more exposed situations, there 

 is g-eneral variation within narrow hmits in both sexes, and the 

 females are generally darker than the males. I have always 

 supposed this latter phase to arise from the fact that the 

 females appear to rest more among the herbage than do the 

 males. On very impure limestones grey forms occur, assimi- 

 lating most perfectly with the limestone ; while on peat, dark 

 peaty-black coloured specimens are found. On slate formations 

 intensely dark slate-coloured or black specimens are the 

 ordinary form, while I have very red specimens from the red 

 sandstone formation. Here is a complete response to environ- 

 ment, and I leave my readers to infer how special races of this 

 particular species have been brought about, and w^hy, on rocks, 

 naturall}- dark or artiiicially darkened by rain, black forms are 

 most generally found. The same line of variation is traceable 

 in Boarniia rcpandata in districts where it settles and rests on 

 the ground, and not on the trunks of trees as is usual with us 

 in the woods of Kent and other southern counties. I have 

 specimens varying in colour exactly in the same way as those 

 of G. obsairata just mentioned, viz., from whitish to black. 

 In these species both the pale and dark races are those which 

 have been developed by " natural selection " in the particular 

 localities in which they are found. Although humidity or 

 wetness, by darkening the surfaces on which the insects rest, 

 would intensify the colour, yet the particular geological forma- 

 tion is here the prevailing factor, or why should we get white 

 forms on the purer cretaceous strata, grey on the impure 

 limestones, red on the red sandstones, black on the slates and 

 schists, and brownish-black on peat ? In short, why is there 

 such a complete response to environment ? Speaking of these 

 leucochroic and melanochroic forms, Dr. Buchanan White, 

 Ent. Mo. Mag., vol. xiii., p. 149, makes the following remarks, 

 which my own observations have since materially borne out. 

 He writes : — " That there is exciting cause for both forms 

 I am persuaded, because we find that species, which are 

 sufficiently common for us to observe year after year in 

 abundance, are found to be much more subject to variation in 

 some years than others ; and if (presumably) the meteorological 

 differences of one year from another, cause, in a single locality, 

 a varying amount of variation in species, we may reasonably 

 conclude that the meteorological differences between one 

 localit}^ 'and another, continued year after year, will tend to 

 variation in different directions in the individuals of a species 



