228 The Inheritance of Wing Colour in Lepidoptera 



the purpose of crossing, by means of larvae or pupae, from Cambridge, 

 Kent and Yorkshire. Notwithstanding this precaution and the fact 

 that the species resists in-breeding very well, all ill-effects were not 

 avoided. In 1916-1917 many of the females became sterile, and the 

 families of others were very small. Dysentery was also severe in 1916 

 and 1917, as may be seen from the small lutea x lutea families in the 

 latter year. 



VII. Beeeding Results. 



The frequency distributions (Figs. 2 — 14) have been constructed from 

 the curves showing the distribution of the colour-values (Figs. 15 — 25) 

 in the manner described on p. 215. The orange colour- values of the 

 parents have been marked with arrows on the scale of colour-units at 

 the bottom of the figures, and the full colour-value has been printed in 

 the margin. When several families are combined in one curve, the 

 arrows indicate the mean orange value of the parents. When both 

 parents are of the same gametic constitution, one arrow refers to the 

 male and one to the female parent. In the case of a cross containing 

 several families, the arrows refer to the varieties of the parents regardless 

 of their sex. The names of all the families included in any curve are 

 printed on the figure, together with the year in which the eggs were 

 laid, thus :— 16 M, '17 E, etc. 



(a) Var. lutea x A. grossulariata. 



For the sake of clearness it is well to divide the colour scale into 

 five arbitrary classes, corresponding to the five columns of insects in 

 Plate IX. This division of the colour scale in both types of distribu- 

 tion curves helps to bring the phenomenon of segregation into evidence. 

 The white or lowest class includes colour-values, from 0*0-0'8, of the 

 type insects (Plate IX, Nos. 25 and 26). The second class, from 0*8-1 '6, 

 are the slightly tinged individuals heterozygous for yellow (Plate IX, 

 Nos. 19 to 24). The third class rather deeper in colour, from 1*6-2*4, 

 is as a rule also heterozygous for yellow (Plate IX, Nos. 13 to 18). 

 It does not contain more than a very few individuals, because it embraces 

 just that part of the scale where segregation takes place, and where the 

 frequency is therefore lowest. The fourth and fifth classes comprise 

 the homozygous yellows, from 2*4-3*2, and from 3*2-4*0, or above 

 (Plate IX, Nos. 1 to 12). 



The i^i heterozygotes lutea x gross, cross can usually be distinguished 

 from the type by slight differences of form or colour. Over a thousand 



