BOARMID.-E—BISTON. 131 



effect that out of dozens of pupa3 collected in recent years 

 none bnt black have been obtained ; by Mr. G. T. Porritt, as 

 to Hudderstield, where all the specimens now appear to be 

 of the black variety ; and now by the Rev. A. Thornley, who 

 tells me that on the borders of Nottinghamshire and Lincoln- 

 shire dark or black specimens only have come under his notice 

 for the last fourteen years. In some parts of Yorkshire and 

 the adjoining counties, and in the Midlands, the two forms 

 seem still to occur in tolerably equal numbers. On the other 

 hand, I hear that the typical insect still prevails in Cumber- 

 land. The black form seems to have reached Berkshire 

 rather early — about 1885 — but the first record that I find in 

 Cambridgeshire is for 1892, Norfolk 1893, Suffolk 189G, and 

 London 1897. About the same time it appears to have reached 

 the New Forest, Hants, but it is still scarce in the South of 

 England. In Scotland, so far as is known, it has not yet been 

 observed ; and in Ireland very rarely. But upon the Con- 

 tinent it has made extraordinary progress ; Dr. August Hof- 

 mann says that in 1884 it appeared near Hanover; before 

 1888 in the Netherlands and Thuringia ; and in the next 

 few years in various parts of the Rhine Valley; indeed, he 

 thinks that its progress was up the Rhine. Further informa- 

 tion shows its general diffusion in the Netherlands and also 

 in Saxony, Silesia, and other parts of Germany. 



This melanic form is itself in some degree variable ; as 

 already remarked, the hind wings have sometimes the front 

 margin white, and even peppered ; the fore wings also are 

 occasionally a little dusted with white, or there is a small 

 indication of a white subterminal line ; and Mr. Sydney 

 Webb has one which shows a deeper black subterminal 

 stripe. Also there is sometimes a tendency to increased 

 size. Mr. G. T. Porritt writes me : " Judging from size, 

 melanism seems to conduce to vigour, for I never remember 

 seeing such enormous specimens as some of these are ; a 

 female looks nearly as big as a poplar hawk ! " 



There still remains another form to be noticed. When the 



