210 The Inheritance of Wing Colour in Lepidoptera 



frequent, often show a change from red to yellow, or from yellow to 

 white, the ground colour alone being affected. I am at present investi- 

 gating several examples of both these varieties. 



The present communication deals with the yellow variety of Abraxas 

 grossulariata, in which the markings are normal, and bright orange or 

 yellow replaces the usual white ground. Little or nothing is known of 

 the pigments involved in such changes, or indeed of any insect pigments, 

 with the single exception of the white and yellow colours of the Pieridae, 

 which Hopkins^ has shown to be due respectively to uric acid, and to 

 some unknown reduction product of the same acid. It is possible that 

 a similar relationship exists between the yellow and white pigments of 

 A. grossulariata ; and if this be so, an enzyme may be found to control 

 the changes in both cases. I hope to be able to undertake a chemical 

 study of the pigments at an early date. 



The experiments were undertaken in order to investigate the genetic 

 relationship of the white and yellow ground colours in crosses between 

 A. grossulariata and its variety lutea. The type insect is usually 

 papery white (see Plate IX, Nos. 25 and 26), or sometimes a very pale 

 shade of cream ; and the depth of the yellow ground in lutea varies 

 considerably. Preliminary crosses showed that the white colour of the 

 type insect was only completely dominant if the yellow of the variety 

 was pale; and it became evident very soon after the experiments 

 were commenced^ that this white colour did not behave as a simple 

 Mendelian character. It is in fact an example of a character which 

 varies more or less continuously; and such cases frequently present 

 problems for which it is difficult to find a satisfactory explanation. As 

 a rule, the F^ heterozygote from lutea x grossulariata is not white, but 

 can be distinguished from the type by a tinge of yellow which 

 occasionally reaches an appreciable depth. The total range of variation 

 in all crosses is considerable, and extends from the papery white of the 

 type insect, through the palest shades of lemon, to a bright reddish 

 orange (see Plate IX, Nos. 1 — 26). 



Since the material could not at once be divided into discontinuous 

 classes, several attempts were made to grade the insects and to place 

 them by inspection in four arbitrary groups. This method had to be 

 abandoned as no reliability whatever could be placed in the judgments, 

 even when these were made under similar conditions of lighting, etc. 

 An instrument of some kind for determining the colour appeared 

 essential, and several were examined for this purpose. The colour- 

 . 1 F. G. Hopkins, Phil. Trans. Vol. 186, Part ii. p. 661, 1895. 



