VIII 
THE COLOURS OF SPIDERS 
179 
abdomen, and the delicacy of the cuticle which 
covers that region. The whole surface of the body 
is not infrequently covered with a dense coating of 
hairs, which are analogous to the scales of Lepido- 
ptera, and are often important in coloration. Accord¬ 
ing to Dr. Henry M'Cook ( American Spiders ), the 
cuticle only contains a relatively small amount of 
pigment, this being chiefly confined to the “soft 
skin ” ( = epidermis ?). 
(1) Optical Colours .—Opinions differ greatly as to 
the prevalence of bright colours in the group, non¬ 
specialists being generally inclined to regard spiders as 
dull-coloured, while enthusiasts like M'Cook and the 
Peckhams speak of them as rivalling insects and 
birds. It is at least certain that metallic colours do 
occur in various species. The commonest of these 
colours appears to be a metallic or silvery white due 
to the structure of the hairs, but in some cases these 
hairs or scales give rise to brilliant iridescence, or to 
pure blue and green colours. In certain instances, 
as for example in the mandibles of Phidippus inorsi- 
tans, the cuticle itself is, as in many beetles, finely 
ridged, and so gives rise to a brilliant green colour. 
In this connection it is interesting to note that the 
Peckhams remark that the bright colours of the male 
are most conspicuous in the anterior region. This 
they ascribe to sexual selection, but if the colours are 
structural they can probably only occur in those 
regions where the cuticle is markedly differentiated, 
and these regions are especially the appendages of 
the mouth and the neighbouring parts. 
(2) Pigmental Colours. —Apart from structural 
colours, those due to pigment seem to be bright and 
