104 COLOUR IN NATURE chap. 



the muscles ; and some earthworms owe their very 

 dark colour to pigment occurring in this situation, 

 or present in considerable quantity in the cells 

 of the peritoneal epithelium. Accompanying the 

 differentiation which gives size and opacity to the 

 body, there is frequently in Annelids, as already 

 noticed, a differentiation of the cuticle which gives 

 rise to structural colour. It is curious to note that, 

 contrary to the usual rule that bright colours in 

 worms when not due to structure are the result of 

 the shining through of coloured internal structures, 

 we find that the bright colours of the little Oligo- 

 chaetes belonging to the genus ^olosoma are . said 

 to be due to coloured oil-globules contained in the 

 skin (see Beddard, Ann. and Mag. Nat. Hist. vol. ix. 

 pp. 12-19). The oil -globules are in the different 

 species blue-green, yellow-greeen, or orange-red, and 

 may be of lipochrome nature. 



As to the pigments themselves, if we bear in mind 

 the statement just made that, when bright, the colours 

 of worms are due in the general case to coloured in- 

 ternal tissues, it must be obvious that the pigments 

 are usually those which by hypothesis are of direct 

 physiological importance. Hemoglobin, which is 

 widely and irregularly distributed in the group, is 

 one of these. It is often exceedingly conspicuous 

 in the more delicate forms ; but even in the larger 

 and more opaque worms it may shine through the 

 thin-walled gills or tentacles. The green pigment 

 which occurs in the blood or coelomic fluid of 

 Sabella, Branchiomma, Spirographis, and Siphono- 

 stoma, is another example. This pigment has been 

 accredited with important respiratory functions. It 



