JOURNAL OF VARIATION. 



No. 5. Vol. I. August 15th, 1890. 



MELANISM AND MELANGCHRQISM IN BRITISH 

 LEPIDOPTERA. 



By J. W. TUTT, F.E.S. 

 {Contiimed frovi page 90.) 



\ATURA non facit saltinii'' is a well-known 

 saying among naturalists. Changes are not 

 brought about in nature suddenly, and in no 

 natural study is the saying more true than in 

 our own interesting pursuit. There is no doubt that the ten- 

 dency to melanism is brought about gradually, when once 

 commenced, by "natural selection," and increased by "here- 

 ditary influence." But I was unprepared for the startling (to 

 me) suddenness with which many species, during the wet 

 season of 1888 assumed a darker colour. In none of the 

 lepidoptera that I met with, was this perhaps more strikingly 

 illustrated, than in Litliosia pyginceola, XylopJiasia nio7ioglypha 

 ipolyodon), Agrotis corticea, and Agrotis tritici, although others 

 showed this influence. L. pygmceola, which is in favourable 

 weather so exceedingly abundant on the sandhills of Deal, is, 

 as is well known, usually of a pale yellow colour in the males, 

 and of a darker shade or grey in the females ; occasionally, 

 however, a darker specimen than usual occurs, showing that 

 there is a tendency in the species to vary in this direction ; but 

 \\\ the summer of 1888 a very large proportion of the speci- 

 mens were exceedingly dark, and I have in my cabinet some 

 strikingly dark specimens, although the species was scarcer 

 than in any year since I have collected at Deal. XylopJiasia 

 iiionoglypha, which is usually of the pale variegated form, with 

 an occasional var. obscm-a, were that year in greater abundance 

 than usual, but almost all were var. obscura, some approaching 



