88 COLOUR IN NATURE chap. 



Similarly, D. ramea also displays the same deep tint 

 whether it grows in shallow water (7-8 fathoms) or 

 at great depths (600 fathoms). 



In connection with the effect of light we may 

 mention the prevalence of blue colours among the 

 pelagic jelly-fish, which many would regard as directly 

 due to the action of light. 



The Pigments of the Ccelentera 



The number, beauty, and great variability of the 

 tints of the Ccelentera make the question of the 

 nature of their pigments one of great interest, but, as 

 is so often the case, the bright pigments are very 

 unstable and their examination is a matter of great 

 difficulty. In consequence, the observations which 

 have been made are, in most cases, very incomplete. 

 We shall not attempt to give a detailed account of 

 the pigments already described, but shall merely 

 describe the characters of the better known of them. 



We have already emphasised the predominance 

 of a green tint in the sessile Ccelentera, and the 

 frequent tendency for this tint to be in whole or in 

 part replaced by another colour, such as blue, pink, 

 or brown. The brightness of the tint has suggested 

 to many the possibility that the pigment might be 

 chlorophyll or some related colouring-matter, impart- 

 ing to the organism the power of taking carbon from 

 the air and evolving free oxygen. Among the more 

 recent supporters of this view we have Prof Hickson, 

 who during his stay in N. Celebes remarked on the 

 absence of Algae in the neighbourhood of coral-reefs, 

 and suggested that their green pigment might enable 



