H. Onslow 



129 



wings. This is more black than is usually found in most type insects, but 

 it is considerably less than that shown in Text-figs. 4 and 6 (about 80 7^), 

 which are constructed from iiusects clearly belonging to dark strains. 

 It is of course probable that there is more than one factor, which by 

 modifying the pattern produce a whole series of insects, in which the 

 area of black varies greatly. 



-:i 100 



"^- 90 



\ J, 



V 18 G Q 9 



^->^ 



-X--. 



M9 zggr-o 



$ Parent of 

 '19 Z 



No. of Insects 

 Text-fig. 1 (cf. Text-fig. 2). Curves showing the distribution of the 

 values of the black pattern in Fi^ ^ and 5 $ from the cross 

 grossulariata $ x varleyata ^ ('19^), which appear to carry L, 

 the factor localising the black pigment. Similar curves are shown 

 for the black values of varleyata in a cross (Fj) $ x varleyata 

 c?('18G). 



The above points are best seen in the frequency distribution diagram 

 (Text-fig. 2). The curves for both the «/'(/' and the $ ? of family 19 Z are 

 similar. They have their maxima at the same point, and they include 

 much the same area. 



In the diagrams showing the frequency distributions the percentage 

 of the black area is given along the base line, and the percentage fre- 

 quency of any given black value is shown on the left-hand side. Thus, 



