1887.] between certain Pupce and their Surroundings. 95 



instances of Pieris brassicce, P. rapoe, Vanessa polychloros, and 

 (erroneously) Papilio machaon. He even suggested that gilded 

 surfaces might probably be found to produce gilded pupae, but the 

 experiment has never been made until the present investigation. His 

 observations were disputed by many entomologists, but were confirmed 

 by Mr. A. Gr. Butler and Professor Meldola (' Zool. Soc. Proc.,' 

 1873). Finally, Mrs. Barber (' Entom. Soc. Trans.,' 1874, p. 519) 

 obtained striking results with the pupae of Papilio nireus (South Africa) 

 which were confirmed by Mr. Roland Trimen, who experimented upon 

 Pajpilio demoleus. Still later Fritz Miiller (' Kosmos,' vol. 12, p. 448) 

 argues that the dimorphic pupae of Papilio poly damus do not possess the 

 colour-relation. It was generally assumed that all the above instances 

 of the colour-relation were to be explained by supposing the skin of 

 the freshly formed pupa to be " photographically sensitive," but the 

 explanation was never tested by any system of transference to other 

 colours, and Professor Meldola pointed out in 1874 that there was no 

 real analogy with photography. Furthermore, the explanation failed 

 to account for the colour of pupae which threw off the larval skin on 

 a dark night. I therefore thought that the problem would probably 

 prove to be essentially physiological, and that the reflected light 

 would be found to act on the larva at some time before pupation 

 and not upon the pupa itself, and it seemed probable that the 

 sensitive area might be defined by experiment. The investigation 

 was conducted in the summer and autumn of 1886. 



I. Experiments upon Vanessa Io. — Material was kindly supplied 

 by Mr. E. D. Y. Pode, of Slade, Ivy bridge. Six mature larvae were 

 placed in a glass cylinder surrounded by yellowish-green tissue-paper, 

 and all suspended themselves from the paper roof. Five changed into 

 the rarer yellowish-green form of pupa, and the sixth immediately 

 after the skin had been thrown off and while still moist and with the 

 shape unformed, was transferred to a black surface in darkness, but 

 the pupal colours deepened into a yellowish-green tint exactly like 

 that of the other five pupae. 



This experiment, so far as it went, confirmed my anticipation of 

 larval as opposed to pupal susceptibility, and added another striking 

 instance of pupal colour-relation. Mr. W. H. Harwood, of Colchester, 

 also informed me that he had found the same variety of this species 

 on the under side of nettle leaves, but not the dark form which 

 occurs commonly on walls, stones, &c. Hence the protective value of 

 the colour-relation is well seen ; the species having varieties suitable 

 for vegetal and mineral surroundings, and adjustable by the stimulus 

 supplied by the colours of the environment. 



II. Experiments upon Vanessa urticce. — This species was investigated 

 in great detail, over 700 individuals being employed in the experi- 

 ments. Material was in part supplied by Mr. Pode, but chiefly 



VOL. xlii. H 



