234 Genetical Studies in Moths 



plant, Galium saxatile, creeps ; in two localities, one in each of the areas 

 I have studied, in Normanby Intake Plantation near Middlesbrough 

 and on Birtley Fell near Newcastle, the melanic race nuhilata is rapidly 

 developing. The case is particularly impressive in the first named 

 instance for, if by any chance the insect rested on bare ground — and 

 I have never seen it do so although I have observed thousands of wild 

 specimens — it would have to sit on a light coloured soil composed of 

 weathered Mgor Grit. And the same applies to the case (amongst 

 others) of Dasystoma salicella, the males of which at Birtley exhibit 

 progressive melanism in spite of their sitting in March on the light 

 yellow grass culms of the previous year; this, too, holds with Xylophasia 

 monoglypha, which almost uniformly hides itself at the base of Nardus, 

 Poa, Brachypodium and similar plants, from which I have often dis- 

 lodged it when in search of Arachnids. 



(5) Furthermore, the same argument demands that melanic forms 

 should not be generated when the insects concerned, whilst yet tree- 

 frequenting, do not rest on dark surfaces ; again the facts directly 

 oppose the theory. 



On Waldridge Fell, in the industrial district of North Durham, 

 there is a colony of Asphalia flavicornis isolated far from any other 

 colony of the same insect. This moth in its typical form has silvery 

 grey wings and sits on birch trunks and twigs. Now the birches it 

 haunts possess the usual silvery bark and purplish twigs, yet the insect 

 there assumes an intensely melanic guise such as I personally have 

 never seen elsewhere ; nor have I seen it referred to in literature. On 

 Eston Moor, where again the birches do not differ perceptibly from 

 those seen by me in secluded Highland glens in Scotland, the insect 

 likewise shows signs, not so emphatic as the fully developed melanism 

 of Waldridge, but still quite unmistakable, of strong melanochroic 

 tendencies. 



To produce another instance is not difficult, although in this case 

 the insect rests on alder leaves. Both in Lonsdale in Cleveland and in 



« 



Chopwell Wood in Durham the moth Melanthia bicolorata is plentiful, and 

 shows a great range of melanic and melanochroic aberrations, and in 

 neither case can smoke blackening explain their dominance. The 

 undersides of the alder leaves are no darker than those in Upper 

 Allendale where the rainfall is 44 inches per annum, and the insects 

 the whitest I know. 



(6) Of the same nature but of different weight is the evidence 

 yielded by woodland insects in the west of Scotland and Ireland. To 



