282 The Inheritance of Wing-Colour in Lejndoj^tera 



should correspond to definite portions of the colour scale, and as far as 

 possible the following values have been taken : 



In the table (p. 286) which shows the F.^ generation, the range of colours 

 is not quite the same, the whole scale being slightly shifted towards 

 the black. 



The white variety is, as has been said, usually imperfectly dominant 

 but sometimes the dominance is complete. The heterozygous males are 

 grey or butf, and in the F^ and other generations, in spite of a considerable 

 variation, the accompanying curves, constructed from the colour values, 

 show that the white and black homozygous insects tend to segregate in 

 accordance with the ordinary Mendelian ratios. The variation of the 

 colour is most probably caused by the presence of a modifying gene or 

 genes, in much the same way as the very variable radiation of the black 



(J cJ parents of Colour Units 



'16 A, '19 B and '16 D 



Fig. 2 (of. Fig. 1). Diagram showing the percentage frequency of 

 the black values of the pure rustica ^ J in the last figure ; as 

 well as of the (J cj in the two (I<\) x rustica families '16 A and 

 '19 B which have been combined. 



