128 The Inheritance af Wing-Colom- in Lepidoptera 



In measuring the black pattern of grossulariata, only the fore wings 

 were considered, since the variation in the hind wings is very slight, as 

 may be seen in the plate. Moreover, only a single wing was measured, 

 since the labour involved is very considerable, and the variation between 

 the two wings of the same insect is usually insignificant. In each case, the 

 sum of the black areas on one fore wing was expressed as a percentage 

 of the total area of that wing ; the values so obtained were then plotted 

 as distributions ^ It at once became evident that there was a factor, L, 

 localising the black pigment to the normal grossulariata pattern of the 

 wings. The effect of I is to allow the pigment to spread, until the fore 

 wings are as black as in var. hazeleighensis. This localising factor L was 

 not always carried by varleyata, the factor I being often introduced by 

 matings with certain dark strains. On account of the increased prices 

 they command, such dark strains are prized by dealers, who would 

 probably pair any varleyata to dark rather than to the ordinary type 

 individuals, in the belief that they would be more likely to produce 

 varleyata in the next generation. It may here be recalled that the 

 factor causing the black rings round the body of var. nigrocincta^, 

 though apparently sometimes associated with var. hazeleighensis, has 

 been shown to be, like the factor I, unconnected with the black variety 

 varleyata. 



Thus many of the F^ families coming from strains of varleyata 

 obtained from Messrs Newman and Porritt show an increased develop- 

 ment of black pigment, which is not apparent in the Fj families obtained 

 from Mr Raynor's strain. Moreover it has been observed that in addition 

 to this factor I, femaleness, or some factor associated with it, prevents 

 the black pigment in the wings of the females from spreading to the 

 extent that it does in the males. A rather similar case has already been 

 described in var. lutea^ in which the intensity of the yellow pigment is 

 considerably lower in the females than in the males. 



Eeference to Text-fig. 1 shows family '19 Z, the ^i generation from 

 a grossulariata $ (33 per cent, black) x varleyata (/. It can be seen 

 from the two curves plotted for a certain number of the cT (/ and $ $ , 

 purposely selected at random, that the extent of the black pattern is 

 practically the same in both sexes. The average amount of the black 

 pattern was found to be about 64 per cent, of the total area of the fore 



1 The method adopted for making these distributions, as well as the percentage 

 frequency distributions, was exactly the same as that described by Onslow, H., Journal of 

 Genetics, Vol. viii. No. 4, p. 209, September 1919. 



2 Onslow, H., loc. cit. ^ Onslow, H., loc. cit. 



