218 The Inheritance of Wing Colour in Lepidoptera 



cross the fit is especially good, the second maximum being no higher 

 on the theoretical basis than on the experimental. In the case of the 

 DR X RR cross, the maxima, especially the second, though no higher, 

 are shifted somewhat to the right. This is no doubt due to the fact that 

 the average colour-values of the parents in the former case are con- 

 siderably higher than the average value of the yellow grandparents of 

 the DR X RR cross, since the yellowest insects were selected for breed- 

 ing. It seems to be fairly clear therefore, from the foregoing considera- 

 tions, that a considerable degree of segregation actually takes place. 



{d) Colour of the hind wings, and effects of desaturation and sex. 



In every case the hind wings are paler than the fore wings, and in 

 a large number of insects separate colour readings were taken of them. 

 In many of the medium and paler specimens the hind wings are quite 

 white, about [I'O: 0-7]^ In the case of one family, '17C (see Figs. 5 

 and 18) the orange values of the hind wings have been shown as a curve, 

 but as no special importance was attached to these figures, elsewhere 

 they have been omitted. On the curve (Fig. 18) it is seen how the paler 

 insects uniformly have white hind wings, irrespective of small differences 

 of colour in the fore wings. 



Mention has already been made of the fact that many of the colour 

 measurements required the inclusion of a small quantity of black, before 

 exact equivalence could be obtained. This amount is very variable, and 

 occurs most irregularly in any series of insects. The highest values are 

 always among the deepest yellows, but even among these there are 

 some devoid of all black pigment. Usually the pale yellow forms have 

 no black, but white insects generally require a small quantity. The 

 deepest yellows no doubt actually contain a little melanic pigment, 

 which under the microscope appears as an almost imperceptible mottling 

 upon the scales. In the white insects the greyish colour of the surface 

 is caused rather by displacement or removal of the scales, than by the 

 presence of lyielanic pigment. These injuries are more apparent in 

 white insects than in yellow ones. Owing to the misleading effects of 

 injury; and to this lack of uniformity in the black values, they were not 

 considered of sufficient importance to record in every case. In family 

 '17 C, however (see Fig. 18), these values have been indicated by means 



^ N.B. All figures in square brackets refer to colour measurements : the first number 

 denotes the orange value, the second number the yellow value. The black values have 

 been omitted. 



