Adjustment of colour in various piqy^, etc. 417 



afford most useful confirmation in the case of a species 

 which has not been hitherto sufficiently tested, besides 

 bringing evidence of its behaviour under conditions as yet 

 hardly tried at all. In the next section is recorded an 

 experiment upon the same species, which, more than all 

 others, needed repetition because of the important con- 

 clusions which follow from it. 



4. Experiments with Conflicting Colours upon the 

 Winter Pup^ of Fieris brassier. (E. B. P.) 



I had long been anxious to repeat some of these experi- 

 ments upon the species of Pi'ej'ma? because of their extreme 

 suitability for such an investigation and because of the 

 important conclusions which follow from the results. 



It had been originally supposed by Mrs. M. E. Barber 

 (Trans. Ent. Soc. 1874, p. 519) that particoloured pupae 

 are produced by a particoloured surface — a conclusion 

 which naturally followed from the views held by many at 

 that time as to a direct " sun-picture or photograph " on the 

 fresh, moist skin of the pupa. A single pupa of Papilio 

 nireus had seemed to support this conclusion. 



In 1886 I made a large number of conflicting colour 

 experiments on Vanessa urticse. (Phil. Trans. 1887, I. c. pp. 

 368 — 392). The contrasted colours were, howevei', only 

 applied during Stage III when the larvje are suspended 

 preparatory to pupation and are less sensitive than at an 

 earlier period. Nevertheless the I'esults were sufficient to 

 make it highly improbable that any parti-coloration of the 

 pupal surface could occur as the result of such a mixed 

 stimulus, and led to the conclusion that the effects were 

 due to the intermediation of the nervous system in the 

 central parts of which the opposing influences from different 

 regions of the body met and produceil more or less of an 

 equilibrium, resulting in the dispatch to all parts of the 

 body surface of stimuli producing intermediate effects. 

 These conclusions were so far-reaching and important that 

 it was necessary if possible to repeat the experiments with 

 other species in which the conditions were more favourable. 

 Although such experiments were not made in 1886 upon 

 the Picrinm, it was clearly seen, when the paper came to be 

 written, that they would be peculiarly suitable for the 

 purpose, because of the great length of the whole sensitive 

 period and the fact that its two stages ai'e both passed 

 under conditions which are eminently favourable for such 



TRANS, ent. soc. LOND. 1899. — PART IV. (DEC.) 28 



