312 MR, E. B. POULTON ON THE COLOUR-RELATION BETWEEN EXPOSED 
Historical. 
The first observation upon the colour-relation between Lepidopterous pupae and sur¬ 
rounding surfaces was made by Mr. T. W. Wood, who exhibited in 1867 a number of 
pupae of P ap'd 10 madia fori, Pieris brassicce, and P. rupee, which corresponded in colour 
to the surfaces to which they were attached (‘Entom. Soc. Proc.,’ 1867, pp. xcix.-ci.). 
ITe also made some remarks on the subject, and expressed his opinion as to the nature 
of the susceptibility of these organisms in the following words :—“ I find as the 
result of my experiments that the skin of the pupa is photographically sensitive for 
a few hours only after the caterpillar’s skin has been shed; and, as might be expected, 
by putting the specimens in the sunshine at the time of changing, and surrounding 
them as much as possible with any desired colour, the most successful results have 
oeen obtained.” There is no doubt that Mr. Wood placed the larvae under the 
conditions he describes, and that in consequence the pupal colours were influenced, 
but if he had transferred the larvae immediately before pupation to a surface of 
an entirely different colour the pupae would have corresponded with the earlier 
surroundings. It seems strange that it never occurred to any previous observer to 
test the theory of pupal susceptibility in this simple manner. Mr. Wood exhibited 
green pupae of P. brassicce, found under a vine on a stone-coloured house, while none 
of the pupae on other parts of the same house were of this colour. Very dark pupae 
were shown which had been taken from a tarred fence, and from other dark surfaces, 
and in subdued light. One of the pupae of this species, found on a white surface, 
was nearly white, and Mr. Wood also showed green, reddish, and dusky pupae of 
P. brassicce on surfaces of similar tints. He also stated that the pupa of Vanessa 
polychloros, when amongst foliage, is coloured like a withered elm leaf, being light 
reddish brown with a cluster of silvery metallic spots (dorsally placed) at the junction 
of thorax and abdomen. He also rightly asserted that the gilded appearance is not 
necessarily connected with the presence of Ichneumon larvae within the pupae. 
When the pupa is suspended to a wall the gilded appearance is not produced, and the 
pupa is of a mottled greyish colour. This observation is very important, for it 
contained the obvious implication that the metallic appearance may be controlled by 
the surroundings, as I have now proved it to be. In fact, Mr. Wood states, “ I feel 
convinced that by the proper use of gilded surfaces the gilded chrysalides of Vanessa, 
and perhaps of other genera, would be obtained, and I hope to be able to try the 
experiment next season.” I was not aware of Mr. Wood’s last suggestion in 1867 
when I undertook my experiments on the subject in 1886, and the arguments which 
induced me to make use of gilded surfaces are given at the beginning of the experi¬ 
ments. It certainly does seem strange that so remarkable, although so bold, a 
suggestion should not have been subjected to any test for nearly twenty years. The 
reason is perhaps to be found in Mr. Wood’s unfortunate inclusion of Papilio machcion 
among the list of susceptible pupae; for Mr. Bond, who knew the habits of this 
