LEPIDOPTEROUS PUP2E AND THETR SURROUNDING SURFACES. 
317 
instead of being hard and dry, became fluid), to a box, of which the two larger 
sides consisted of white gauze, and the narrower sides and the bottom and top 
(cover) of grey pasteboard. They fastened themselves to a thin defoliated stalk of 
Aristolochia. Of the five larvae, two changed into brown and three into green pupae ; 
a brown and green pupa were on the same stalk, removed by less than their own 
length from each other. They emerged from the egg at the same time and shed their 
larval skin at the same time, whilst during their whole life (larval) they were 
exposed to the same external conditions, the same action of light, and to the time of 
pupation had neither brown nor green in their surroundings. In this case, therefore, 
the influence of the colour of the environment certainly cannot have affected the 
colour of the pupa.” (‘ Kosmos,’ vol. 12, p. 448.) 
Previously accepted explanations . 
The theory of the moist, fresh, pupal surface as “ photographically sensitive ” was 
obviously a metaphor borrowed from the sensitive plate of photography, and Professor 
Meldola pointed out that there could be no real analogy between the two processes. 
Furthermore, there was the difficulty that the explanation failed to account for the 
colour of those pupae which throw off the larval skin on a dark night, for the pupal 
colours very quickly deepen into their permanent condition. Considering these 
difficulties, and knowing that the explanation had never been tested by “ transference ” 
experiments, I came to the investigation with the firm conviction that it would be 
found that the problem was essentially physiological, and that the physico-chemical 
changes were merely the results of far more complicated physiological processes. It 
furthermore seemed probable that the reflected light would be found to act—for a 
period long enough to include, under any circumstances, many hours of daylight— 
upon some sensitive area in the larva as it rested upon a coloured surface before 
pupation, and it appeared likely that such a sensitive area might be defined by 
experiment. The investigation was conducted during the summer and autumn of 
1886. The object of the present paper is to give an account of the investigation of 
the questions alluded to above, and its results are therefore preliminary in the sense 
that they afford a foundation for future work, in which the physiological changes 
induced by varying colour must be sought out by histological and other methods. 
Such an investigation I hope shortly to undertake. 
Experiments upon Vanessa lo. 
This pupa is dimorphic, the common form being “ pale grey, but freckled all over 
with smoky black” (Buckler), with a small amount of gilding, while the less common 
form is bright yellowish-green, with a large amount of gold. I determined to 
ascertain whether the latter form could be produced by placing the larvae in 
