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MR. E. B. POULTON ON THE COLOUR-RELATION BETWEEN EXPOSED 
The observations upon the length of the preparatory period and of its constituent 
stages were insufficient, but they indicate a much greater length than in the case of 
V. urticce. In most cases the period began when the larvae were placed in the 
cylinders, &c., for no food was eaten by the majority of larvae after they had been 
captured. This was because I always selected the largest larvae from the cabbages 
and, as was previously explained, the shock of capture hastens the beginning of the 
period when the organisms are practically mature. 
It is also noteworthy that there are some indications, as in the case of V. urticce, 
that darkness may act in such a way as to prolong the whole period, and that 
possibly this increased length of time may bear upon the formation of pigment; or, 
conversely, that a shortened period may be brought about by certain reflected colours, 
and that the absence of pigment may ensue as a secondary result. This suggestion 
appears to be worth a careful trial, and, even if it does not contribute to the elucidation 
of this most difficult question, the protracted period in darkness may be useful to the 
organism in another way—to give it the opportunity of being affected by surrounding 
colours after change in the conditions of illumination. Thus, if the most sensitive 
part of the period were passed dining the night, it would be to the advantage of the 
species for such a susceptible condition to be prolonged as far as possible. It mav be 
that the absence or presence of direct light may be important in this respect, but 
the whole subject needs careful experimental investigation along the lines suggested 
by the results of the experiments described above. 
Series 2.—Pupje found upon Various Surfaces of Mixed or Indefinite 
Colours. 
A certain number of wild pupae were found upon walls, cement, &c., of colours which 
were not distinct enough to be included in the last series ; and a large number of 
captured larvae were allowed to pupate without any precautions to ensure uniformity 
in the colour of surrounding surfaces. 
The results are described below :— 
I. Mr. Harwood also sent me two pupae of P. rapce, found upon a cemented wall. 
They were both (3), with a distinct pinkish ground-colour, and one of them with 
unusual development of black patches on the dorsal surface generally, without any 
special development on the ridges and keel. These colours would be of protective 
value against the greyish surface. 
II. September 20. Two pupae of P. rapce were found fixed to some yellowish-grev 
brick gate pillars, but shaded under the coping, at Yarbridge (Isle of Wight). 
Of these.1 was (3), pinkish, lighter than usual. 
1 ,, (4), pinkish, unusually grey, but with a smaller amount of 
pigment patches than usual. 
The pupae were well protected, for their colour harmonised with that of the 
bricks, &c. 
