102 
COLOUR IN NATURE 
CHAP. 
due to a system of fine lines on the surface. With 
the greater development of the cuticle in the marine 
worms, there is also a greater elaboration of struc¬ 
tural colour. 
As a type of coloration in Polychaetes we may 
ake Nereis diversicolor , a very common worm on 
our shores. This species shows considerable colour- 
variation, the upper surface being a pure bronze, 
greenish-brown, green, or pinkish, while the lower 
surface is bright pink or flesh-coloured, the whole 
body showing a very distinct metallic sheen in 
addition. These bright colours are most distinct in 
the large adult specimens found in the Laminarian 
zone, and fade very rapidly after death, whether the 
specimens are preserved in alcohol or formalin. 
Preserved specimens are dead-white in colour, but 
still show a faint sheen. 
Taking such a form as a starting-point, we have 
on the one hand worms in which the colour is 
predominantly structural, and on the other those in 
which it is predominantly pigmental. Structural 
colours are especially marked in cases where the 
characteristic bristles attain great development. In 
the sea-mouse (. Aphrodite ), for example, the bristles 
form a dense felt-like mass exhibiting beautifully 
iridescent tints, which are in life much obscured 
by the mud with which the animals are usually 
covered. The beautiful golden crown of bristles 
which Pectinaria belgica protrudes from its tube, 
is another example of structural colour occurring in 
connection with specialised cuticular structures. 
Colours due to pigments are also often exceed¬ 
ingly beautiful in these marine worms. The vivid 
