1887.] between certain Pupce and their Surroundings. 107 



3. The Length of the Preparatory Period.— The observations were 

 not sufficient to determine the duration of the periods and of its stages 

 with any great accuracy, but all the experiments render it certain 

 that the length is much greater in both species than in V. urticce. 

 There were also some indications, as in V, urticce, that darkness may 

 cause the prolongation of the period. 



4 Blinding Experiments. — The larvae of P. rapce were alone made 

 use of, and they are as well suited to this method of investigation as 

 P. machaon. The sets of pupae produced from normal and blinded 

 larvae were very similar, and thus the results harmonise with those of 

 all the blinding experiments in other species of larvae. 



5. Transference Experiments. — A considerable number of the larvae 

 of P. rapa were transferred for the whole or part of Stage (iii) 

 to a surface of a colour different from and generally opposite to that 

 which had previously influenced them, and the results entirely har- 

 monised with those previously described in other species, showing 

 that the larva is sensitive and not the pupa, and that the time of 

 greatest susceptibility is before Stage (iii), or only including the first 

 part of it, but also rendering it probable that the larvae can be 

 influenced to a small extent during this stage. 



6. The Nature of the Effects wrought upon , the Pupce. — The varied 

 pigment effects which follow the influence of different surrounding 

 colours are attended by other more deeply seated changes of 

 even greater physiological interest and importance. The black 

 pigment patches and minute black dots are cuticular and super- 

 ficial, while the green, pink, or other ground colours are subcuticular 

 and deep-seated, and in the most brightly coloured pupae they are 

 mixed colours, due to the existence of different pigmentary (and 

 probably chlorophylloid) bodies present in different elements and at 

 different depths in the subcuticular tissues of the same pupa. In 

 other pupae no trace of such colours can be seen. Hence we see in 

 these most complex and varied effects of the stimulus provided by the 

 reflected light, which deepen into their permanent pupal condition 

 very many hours after the stimulus has ceased to act, the strongest 

 evidence for the existence of a chain of physiological processes 

 almost unparalleled in intricacy and difficulty, while a theory of 

 comparatively simple and direct photochemical changes induced by the 

 stimulus itself, without such a physiological circle, seems entirely 

 inadequate as an explanation of the facts, a conclusion which is borne 

 out by a comparison with the experiments upon other species described 

 in this paper. 



VI. Experiments upon Ephyra pendularia. — After the consideration 

 of the many species of variable pupae of the Rhopalocera, it is of inte- 

 rest to compare the results of the investigation of the equally exposed 

 and variable pupae of certain species of a single genus of Heterocera, 



