318 MR. E. B. POULTON ON THE COLOUR-RELATION BETWEEN EXPOSED 
appropriate coloured surroundings before pupation. Mr. E. D. Y. Pode veiy kindly 
sent me six nearly full-grown larvae from South Devonshire, and these were placed in 
a glass cylinder covered with two thicknesses of green tissue paper, of w T kich the 
outer layer had become very yellowish from the action of light. The paper being 
very transparent, the larvae in the cylinder were exposed to a yellowish-green light, 
mixed with a great deal of white light. All the six larvae suspended themselves from 
the paper roof of the cylinder, and five changed into the yellowish-green variety. One 
of these was figured (see Plate 26, fig. 7 ; natural size). The sixth was detected a few 
minutes after the larval skin had been thrown off, for the surface was moist and the 
shape unformed. It was exactly in the condition of assumed photographic sensitive¬ 
ness, described by previous observers. I therefore cut it down immediately and pinned 
it up in an opaque box with a tightly fitting lid, the whole interior surface being lined 
with black paper. In a few hours I opened the box, and found the pupa a yellowish- 
green variety, exactly like the others. It is therefore quite clear that the influence had 
worked previously—during the larval stage. There can be no doubt that this result 
without a single exception, is conclusive, when the comparative rarity of the green 
variety is considered. In all my previous experience I have only obtained this variety 
singly among large numbers of the dark form, and I have never seen it among the 
numerous pupae found upon palings and walls, and I have never found the pupa of this 
species in other situations—-upon the leaves of its food-plant or other plants. Being 
anxious to ascertain whether other observers have had the latter experience, and to 
know its results, I wrote to Mr. W. H. Harwood, of Colchester, who has been a most 
keen observer for many years. In his reply he says, “ I have sometimes found the pale 
form of Io on the under-side of nettle leaves, but do not remember meeting with the 
dark one.” From this observation it is seen that the power of colour adaptation, 
which experiment has proved to exist in this species, is actually turned to account in 
the wild state. Newman, in ‘British Butterflies,’ p. 61, does not recognise the pupal 
dimorphism, for he says, “ the colour of the chrysalis is green; as the chrysalis 
darkens its colour deepens, but the green tint is never entirely lost.” Buckler, 
on the other hand (Bay Society, 1885), fully recognises the two forms. While the 
single individual, which was transplanted to a colour which must presumably tend 
towards an opposite effect, seems conclusive against the former theory of pupal as 
opposed to larval sensitiveness, the same results are better seen in Vanessa urticce, 
where they were worked out in great detail, and in which the proof becomes 
irresistible from the large numbers employed in the experiments. The cuticles of the 
left pupal wings of the two varieties are figured in Plate 26, figs. 10 and 11, both X 7, 
and the immense differences in the tint of the cuticular ground colour and the amounts 
of pigment present are well seen. 
