io6 COLOUR IN NATURE chap. 



The other pigments of the bristle-bearing worms 

 are not well known ; it is possible that some of the 

 pink pigments are lipochromes. 



As to the colours of Polychaetes in general, the 

 striking features are the presence of optical colours, 

 the number of green forms, and the absence of those 

 beautiful and elaborate markings which are so char- 

 acteristic of the leeches. The plan of the colora- 

 tion is throughout much simpler ; when brilliant, 

 it seems to be usually dependent upon coloured in- 

 ternal tissues shining through the skin. A great 

 number of forms, moreover, especially those inhabit- 

 ing tubes, are colourless and transparent. 



The colours of the Oligochaetes, such as the earth- 

 worm, hardly merit separate notice : they are mostly 

 dull or inconspicuous, but in some cases show a 

 tendency to develop simple patterns. Of this tend- 

 ency our own brandling {Lumbricus fcetidus) affords 

 a convenient example. 



The Pigments of the Capitellid^e 



The pigments of the small group of Polychaetes 

 known as the Capitellidse are perhaps worthy of more 

 detailed notice. The Capitellidae are the subject of 

 one of the large Naples monographs, and the author. 

 Professor Eisig, makes some observations on their 

 colours which have been very widely quoted. The 

 Capitellidae are remarkable among Annelids in 

 having no closed blood-vascular system, the blood 

 being contained in the general body cavity. Ac- 

 cording to Eisig, it always contains haemoglobin, and 

 is of a bright red colour which directly affects the 



