The most striking and familiar case is that of _Amphidasys betularia_, of which only the ordinary type was known in any locality until about 1848-1850, when the totally black var. _doubledayaria_ first appeared in the neighbourhood of Manchester. This black form was subsequently recorded in Huddersfield between 1860 and 1870; Kendal about 1870; Cannock Chase, 1878; Berkshire, 1885; Norfolk, Essex and Cambridge about 1892; Suffolk, 1894; London, 1897. For the Southern Counties of England, except in the London district, there are still very few records. It cannot of course be asserted positively that the variety spread from its place of first appearance into the other localities, and that it did not arise _de novo_ in them, but there can be little doubt that the process was one of colonisation. On the European Continent the first records are from Hanover in 1884, Belgium 1886 and 1894, Crefeld 188-, Berlin 1903, Dresden about the same date. As regards the increase of the variety we have the fact that in Lancashire, Cheshire and the West Riding of Yorkshire the black is now the prevalent form; and in some places, as for example, Huddersfield, the black alone is now found, though it was unknown there till between 1860 and 1870. About 1870 at Newport, Monmouth, the two forms were in about equal numbers, but a few years later the type had almost vanished. Similarly in Crefeld, where the black form was still very rare in the eighties, it now forms about 50 per cent. of the population. In the London district the black remains scarce and at the date of the report it was still very scarce. From Ireland there is only one record and there are hardly any from Scotland. _Boarmia repandata_ is another species which is behaving in a somewhat similar way. Unlike _betularia_, however, the species is a variable one, and has several colour-forms, amongst them the banded var. _conversaria_, and many others. In addition to these there is a black form in the North of England which seems to be spreading. In Huddersfield the black was first recorded in 1888, and in 1900 20-25 per cent. were black. At Rotherham the black or very dark are now prevalent and have increased in the last 15 years. From the Midlands, East Anglia and Southern Counties the returns show only the light and medium forms. Of _Odontoptera bidentata_ several intergrading dark forms exist, and these are found exclusively in the North and the Midlands. Unicolorous blacks have been found recently in the Lancashire mosses and at Wakefield. At Huddersfield 50 years ago the light forms were prevalent, but now a rather dark brown, not infrequently suffused with black, is the commonest. In Southern Counties only light forms are known. _Phigalia pilosaria_ in South England is always light, but in the North the prevalent form is darker. About 35 years ago a form with unicolorous sooty fore-wings and dull grey hind wings was first seen in Yorkshire and a similar form is now taken regularly in South Wales.