I02 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 elaboratign 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- 

 Veiriation, 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 attciin 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 structured colour occurring in 

 connection with specialised cuticular structures. 



Colours due to pigments are also often exceed- 

 ingly beautiful in these marine worms. The vivid 



