vni 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 T)\ 



( 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 morsi- 

 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 



