96 Mr. E. B. Poulton. On a special Colour- Relation [Feb. 10, 



found near Oxford. The first necessity was the construction of a 

 standard list of colours with which to compare the pupae which had 

 been the subjects of experiment. The pupae are very variable, and in 

 many of the experiments the colour influence was only allowed to act 

 during a small part of the time during which the larvae are sensitive. 

 Hence the careful record of minute differences was absolutely 

 necessary, and the standard list was made as detailed as possible. 

 The list was as follows : — 



The degree of colour represented by — 



(1.) Very dark, from the large amount of cuticular pigment; no 

 gilding or the merest trace. 



(2.) Dark normal form, but not so black as (1) and sometimes more 

 gilding but very little. 



(3.) Light normal form, sometimes with a fair amount of gilding, 

 often with a predominant pinkish tint. This degree was afterwards 

 subdivided into dark (3), (3), and light (3), and even further in 

 certain experiments. 



(4.) Very light variety, often extremely golden; sometimes light 

 pink. 



(5.) The lightest variety ; often completely covered with the gilded 

 appearance. 



In the experiments summarised below, the individuals belonging to 

 different companies were always separated, except in the larvae 

 subjected to green surroundings, so that the errors from varying 

 hereditary tendencies were reduced to a minimum, for the larvae of 

 each company are hatched from the eggs laid by a single butterfly. 



1. The Uesults of Different Colours. — Orange surroundings produced 

 no effect, as far as the experiment went, for the few pupae were all (3) 

 and therefore showed no relation to the colour of the environment. 

 After the experiment upon the allied V. Io I tried the effects of green 

 upon a large number of individuals, but the resulting pupae were on 

 the whole rather darker than usual, probably because of the amount of 

 shade produced by the tissue-paper. This conclusion suggested the 

 use of blach surroundings, and at once an immense effect was witnessed. 

 These effects in turn suggested the use of white surroundings (white 

 paper and white opal glass) and here also a powerful influence was 

 exerted, the pupae being often brilliantly golden in appearance. But 

 it was clear that the very dark varieties were much better protected 

 against the black surfaces than the lustrous golden pupae against the 

 white surfaces, and this consideration suggested the use of a material 

 with which the golden appearance harmonised most perfectly, *.e., 

 metallic gold. Boxes and cylinders lined with gilt paper and turned 

 towards a strong light produced the most extremely gilded varieties in 

 a large proportion of the pupae, and the metallic appearance was 

 yellower and more trulv golden than in the more silvery forms 



