PELAGIC FORMS COLOURING 29 I 



Whereas most worms live at the bottom of the sea, at various 

 depths, a few are to be found at the surface. Purely pelagic 

 habits are confined to a few families, viz. Tomopteridae, 

 Typhloscolecidae, and the Alciopids and others amongst the 

 Phyllodocidae ; though Xcctochaeta, one of the Polynoidae, and 

 Ophryotrocha, one of the Eunicidae, are modified for this mode 

 of life. 1 Several genera become pelagic during the breeding 

 season. All these forms are excellent swimmers, and many 

 of them are transparent. 



The Colouring of Polychaetes. The majority of Polycbaetes 

 quickly lose their colour in spirits, and become uniformly dull or 

 light brown in museums. There are a few, however, which retain 

 their brilliancy, like Aphrodite and Chloeia, but in both cases the 

 coloration is due to the beautiful hair-like bristles ranged along 

 each side of the animal; in the former the colours of the rain- 

 bow flash from specimens which have been kept in spirit for any 

 length of time. The Polynoids, too, with their golden chaetae 

 and pigmented scales, retain to some extent their characteristic 

 colouring. But the colours of most Annelids are due to 

 pigments in the skin, together with the haemoglobin of the 

 blood, which are soluble, or otherwise changed, in alcohol ; for 

 instance, the bright greenish-blue tint of the common Pliyllodoce 

 of our coasts is changed to a rich chocolate brown ; but such 

 cases are rare, most worms becoming more or less decolorised. 



The varied colouring in the rolychaetes, as in other animals, 

 is due to a variety of causes. The red is in many cases due to 

 haemoglobin of the vascular system showing through the trans- 

 parent body ; the green of the tentacles of the Sabellids and 

 Chlorhaeniids is similarly due to chlorocruorin. In other cases 

 the contents of the intestine or the tint of the coelomic fluid 

 may affect the colour of the worm. In Capitella the coloured 

 excretory products are retained in the skin ; in an Eunicid 

 living in a yellow sponge, on which it feeds, the colour- 

 ing matter is extracted and stored in the skin ; in the same 

 kind of way green caterpillars may owe their tint to feeding on 

 green leaves. But many of the Polychaetes possess distinct 

 pigments in the skin ; thus in Arenicola the dark pigment 



1 For pelagic forms, see Camille Viguier, Arch. de Zocl. Bxpir. (ser. 2) iv. 1886, 

 p. 347 ; also Reibisch, Die pclag. Phyllodocidcn u. Typhloscolcciden d. Plankton 

 Exped. 1895. 



