One of the most remarkable evolutionary processes, the more striking since it has occured before our eyes, has been the rise and spread of melanism and melanochroism amongst the Lepidopetera. Commencing about 1850 in the Manchester area in England with the Geometrid moth
Amphidasys betularia
L., which yielded the black form
carbonaria
Jord. (
doubledayaria
Mill.), this development has proceeded so rapidly, and become so widespread, that now there is scarcely a country in Northern and Central Europe which does not produce its quota of melanic insects. Moreover, the same state of affairs exists in the North-Eastern United States, although there the number of species affected, up to the present, is not so great as in Europe. Another important feature about these changes lies in the circumstance that, almost uniformly, in Europe and in the United States, the first species to exhibit melanism in any given area have been
Amphidasys betularia
and
Tephrosia crepuscularia
. From the beginning, the Geometridæ, more especially the subfamily Boarmiinæ, have provided not only the bulk of the melanic varieties, but also the greatest numbers of individuals. In many areas, as for example in the case of
A. betularia
and
Y psipetes trifasciata
, only black examples occur. Nevertheless, other groups include species which have gone black; for instance, the Noctuidæ present black forms of
Aplecta nebulosa
Hufn., the Cymatophoridæ of
Cymatophora
or F., the Arctiidæ of
Spilosoma lubricipeda
L., the Gelechiidæ of
Chimabacche fagella
F., and so on.
The recent development of melanism in the larvæ of certain species of Lepidoptera, with an account of its inheritance in
Selenia bilunaria
esp