236 The Inheritance of Wing Colour in Lepidoptera 



under, whereas in Fig. 17 there are about 1 per cent. But since the 

 maximum frequency for heterozygous j^ellows (about 1*0) lies so close to 

 that of the white type insects (about 0-6 or 0*7), the ability to distinguish 

 colours is not sensitive enough to permit of the two maxima being 



2 3 4 5 Colour-units 



[1-0: 0-9] [1-1: 0-9] 



Mean col our- values of 



hybrid parents 



Fig. 10. (Cf. Fig. 22.) Curve showing frequency distribution of the orange 

 and yellow colour-values of the offspring from 16 pairings of hybrid 

 {lutea X gross.) x hybrid {luteax gross.). 



separated. Segregation between the heterozygous and pure yellows is 

 distinct, though the frequency of the yellows does not reach a very 

 pronounced maximum. The expected ratio, 25 : 75, is in this case 

 exactly the observed ratio. It must not be forgotten that the length 

 of the colour scale occupied by the yellow class is as great as that 

 covered by both the type and the heterozygous classes, but it is the 

 area of the curve not the height which corresponds to the number of 

 individuals it contains. Some of the extracted yellows are very deep 

 in colour, almost as dark as a pure-bred yellow, but the average orange 

 colour-value (about 3'0) is rather less than what it is for pure yellows 

 (about 3-6). 



Figs. 11 and 12 are made from two fairly large families of the same 

 type of cross. Fig. 11 is in most details similar to Fig. 10 except that 

 both the yellow and orange curves rise to rather a sharper second 

 maximum. Fig. 12 is not so characteristic because the family is only a 



