132 COLOUR IN NATURE chap. 



bergi has similar blue spots arranged in radiating 

 lines. In Diadema the spots have been called eye- 

 spots. 



4. Crinoids. — The Crinoids are remarkable in 

 showing great individual variation in colour. During 

 life the colours are usually brown, red, purple, violet, 

 green, yellow or white, but the curious form called 

 Holopus is of a jet-black colour. Agassiz remarks 

 that the colours of the deep-sea and shallow-water 

 forms show remarkable similarity. 



As to individual variation in colour Moseley notes 

 that during the voyage of the Challenger he found 

 specimens of Pentacrinus which were purple, and 

 others which were yellow or pale-coloured. Agassiz 

 noticed the same thing in both Pentacrinus and 

 Rhizocrinus, while Malard describes it in greater 

 detail for Comatula. Malard found a large number 

 of specimens of the rosy feather-star on a buoy near 

 La Hougue which were of three distinct colours, 

 violet-red, orange-red, and white and red with reddish 

 pinnules. Clinging to the feather-stars, Malard found 

 numerous specimens of the Crustacean Hippolyte, 

 and he states that " at least in the majority of 

 instances " the prawns resembled their neighbours 

 so much in tint that it was exceedingly difficult to 

 distinguish them. Malard regards this as an ordinary 

 case of colour resemblance, but it is also interesting 

 on account of the numerous analogies which exist 

 between the colours of the Echinoderms and the 

 Crustaceans. We find in the two groups not only 

 similar colours, but also a similar range of variation. 

 As we shall see, the variation in Crinoids is not 

 merely apparent, but is a question of pigment. 



