198 DARWINISM chap. 



from dusky through pinkish to pale green. It is interesting 

 to note, that the colours produced were in all cases such only 

 as assimilated with the surroundings usually occupied by the 

 species, and also, that colours which did not occur in such sur- 

 roundings, as dark red or blue, only produced the same effects 

 as dusky or black. 



Careful experiments were made to ascertain whether the 

 effect was produced through the sight of the caterpillar. The 

 ocelli were covered with black varnish, but neither this, nor 

 cutting off the spines of the tortoise-shell larva to ascertain 

 whether they might be sense-organs, jiroduced any effect on 

 the resulting colour. Mr. Poulton concludes, therefore, that 

 the coloui'-action probably occurs over the whole surface of 

 the body, setting up physiological processes which result in 

 the corresponding colour-change of the pupa. Such changes 

 are, however, by no means universal, or even common, in 

 protectively coloured pupae, since in Papilio machaon and 

 some others Avhich have been experimented on, both in this 

 country and abroad, no change can be produced on the pupa 

 by any amount of exposure to differently coloured surround- 

 ings. It is a curious point that, with the small tortoise-shell 

 larva, exposure to light from gilded surfaces produced pupae 

 with a brilliant golden lustre ; and the explanation is supposed 

 to be that mica abounded in the original habitat of the species, 

 and that the pupae thus obtained protection Avhen suspended 

 against micaceous rock. Looking, however, at the wide range 

 of the species and the comparatively limited area in which 

 micaceous rocks occur, this seems a rather improbable ex- 

 planation, and the occurrence of this metallic appearance is 

 still a difficulty. It does not, however, commonly occur in 

 this country in a natural state. 



The two classes of variable colouring here discussed are 

 evidently exceptional, and can have little if any relation to 

 the colours of those more active creatures which are continu- 

 ally changing their j^osition with regard to surrounding objects, 

 and whose colours and markings are nearly constant through- 

 out the life of the individual, and (with the exception of 

 sexual differences) in all the individuals of the species. We 

 will now briefly pass in review the various characteristics and 

 uses of the colours which more generally prevail in nature ; 



