280 The Inheritance of Wing-Colour in Lepidoptera 



In these circumstances a large number would pupate successfully, but 

 next year only from 25 to 50 per cent, would emerge. When the disease 

 appeared some time before pupation, the case was usually hopeless, and 

 the family was thrown away to prevent further infection. From the limp 

 and disintegrating look of the sick larvae the disease appeared as if it 

 might be due to a proteolytic bacterium, but smears of the blood failed 

 to show any definite organism. It was possible, however, that the ex- 

 amination was not made at a sufficiently early stage. 



The ^1 cTc/* hybrids from the first cross of rustica x type, like those 

 of previous observers, varied from cream to a dark buff (see Nos. 3 to 7, 

 PI. XXVII),but were sometimes milk white like var. rustica, or white with 

 a fleck or two of grey, especially on the hind wings (see No. 8, PI. XXVII), 

 but the range of colour was considerable. In order to classify these 

 intermediate forms for analysis, it was necessary to give them definite 

 colour values, which was done by means of the tintometer in the manner 

 previously described^ To match the various shades of grey it required 

 approximately the same number of units of blue, red and yellow. In the 

 case of the dark insects orange-red predominated, and in the case of the 

 cream and butf coloured insects, orange-yellow. The following table gives 

 the colour values of some characteristic insects : 



Unfortunately there Avere a certain number of insects which had light 

 veins (cf. No. 6, PI. XXVII) and others which showed a central area paler 

 than the periphery (cf No. 3, PI. XXVII). It at first appeared very diffi- 

 cult to give such insects a value which would represent the mean colour, 

 but after several attempts the following method was adopted. One or 

 both wings were removed from the body and mounted at the centre of 

 a large cork, which was then fitted to the shaft of an electric motor. On 

 revolving the motor at a sufficient speed, the markings on the. wings 

 blend, as on the colour-wheel, into a uniform field, which can be measured 

 by the tintometer in the usual way. • 



From the values in the table above it is clear that the figures for 

 orange and yellow are small enough to be insignificant, and since their 

 ^ Onslow, H., Journal of Genetics, Vol. viii. p. 225, September, 1919. 



