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, produced any effect on 
the resulting colour. Mr. Poulton concludes, therefore, that 
the colour-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 which 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 when 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 position 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; 
