98 COLOUR IN NATURE chap. 



worms. The richest purples appear on velvety skins 

 of deep brown or black, each of the soft and mobile 

 folds giving shades that vary in intensity and lustre. 

 Bright yellow contrasts with dark brown, white with 

 vermilion brown and dull pink, while individual 

 uniformity is characterised by such hues as rose- 

 pink, white, green, yellow and olive, the gradation of 

 colour in the various parts of a single specimen 

 being so subtle that enthusiasm as well as skill is 

 necessary in the artist who sets himself to the task 

 of faithful delineation " {Ray Soc. vol. xxxiv. p. 2). 

 This description is based on the British forms only, 

 and the tropical are said even to surpass these in 

 splendour. In addition to the beauty of colour, 

 we find that simple forms of marking, such as 

 longitudinal and transverse stripes, are common. 

 Professor MTntosh speaks also of the "silver sheen," 

 and the " ever-changing iridescence of the active 

 cilia," and considers that in point of beauty and 

 variety the Nemerteans even surpass the Annelids. 

 Light seems to have some influence on colour, but 

 the exact extent of the influence is apparently not 

 determined. Thus we are told that some of the 

 most brightly coloured live in crevices and dark 

 corners, but that under natural conditions the colour 

 varies according to the amount of exposure to light. 

 In captivity Lineus marinus turned pale, especially 

 in the anterior region, but others, e.g. Amphiporus 

 lactifloreus, developed more pigment so that the skin 

 became opaque and of a deeper colour. Some are 

 transparent, and the food contained in the gut 

 (Algae, etc.) shines through and produces a marked 

 and peculiar coloration. There is virtually no sexual 



