64 BRITISH LEPIDOPTERA. 



more generally developed in species that rest on fences, the trunks of 

 trees, the faces of rocks, or on the ground, than in other species. It 

 may, of course, be assumed that those usually found upon fences were 

 originally confined, more or less, to tree-trunks, and that the influences 

 acting upon one are equally potent on the other. 



It has been observed that, in a great number of species of moths 

 that rest on fences and tree-trunks, and are more or less abundant in 

 the London district, the individuals are darker in colour than those of 

 the same species, captured a few miles outside the metropolis. This is 

 clearly observable in Triaena psi, Haneropkila abruptaria, Acidalia 

 I'irynlaria, Eupitkecia rectangulata, ^Iclanippe fluctuate, Boarmia yem- 

 maria, Hybernia defoliaria, H. marginaria, H. leucophaearia, Oporabia 

 dilutata, Diurnaca fagella, Tortrix podana, Hedya occllana and many 

 other species. 



There can be no doubt that in the suburbs of London, fences and 

 tree-trunks are generously covered with soot. (Those who have green- 

 houses, and attempt to keep the white paint clean, will understand how 

 completely they are covered). The tree-trunks have become darker 

 during the last fifty years, and the depth of colour is gradually increas- 

 ing in what were then suburban districts. The pale grey and ochreous 

 specimens of the insects just named used to be well protected 'on their 

 then clean resting-places. Such specimens are now exceedingly con- 

 spicuous when they occur, which they only occasionally do, for the selec- 

 tion of the darker specimens for preservation by nature, has resulted 

 in the permanent darkening of the race. But it is in the manufacturing 

 districts in Yorkshire, Lancashire, Cheshire, Derbyshire, Notts, Staf- 

 fordshire, South Wales, etc. where thick smoke is poured from number- 

 less chimneys, and where the fences, tree-trunks, and even the surface of 

 the ground are begrimed with soot, that the most marked cases of 

 what may be termed protective melanism occur. There we get the 

 "Negro" aberration (ab. doubledayana) of Amphidasys betularia, the 

 ab. niijra of Tephrosia creptuctdaria (biundularia), the ab. fmcata of 

 Hybernia marginaria, the ab. obscura of Epunda riminalis, the ab. niijra 

 of Boarmia repandata, whilst many other species give absolutely black 

 aberrations, which are rarely observed elsewhere. These black aberra- 

 tions, it is well-known, have practically come into existence during the 

 last half-century, and their range is rapidly extending. So completely, 

 too, are many of these dark aberrations supplanting the type that, in 

 some localities, the pale typical forms are almost unknown. These 

 moths are nearly all essentially grey that is, black and white in their 

 typical forms. The gradual darkening of the tree-trunks, etc., by the 

 deposition of soot, has resulted in the better protection of the darker 

 specimens, and hence their better preservation, and, as we have just 

 hinted, the trunks and fences have become so blackened that, in some 

 districts, the absolutely black specimens comprise the best protected 

 form of the species. 



Parallel, if not absolutely identical, with this form of melanism is 

 that exhibited by those species that rest on rocks. Certain Alpine 

 species exhibit this form of melanism in a most marked manner, both 

 in the mountains of Europe and N. America. Certain species that 

 rest on peat are black, wherever they may be found, and however 

 different may be the meteorological conditions of the various districts 

 they inhabit. On the peat bogs in the New Forest, Gnopkos obscwata 



