82 COLOUR IN NATURE chap. 



polypes, but owing to the way in which these are 

 spread over it, they have a superficial appearance of 

 enclosing the coral within their own soft parts. 



Distribution of Colours 



The coral-reefs of warm seas are largely formed 

 of such colonial sea-anemones, the simpler colonial 

 forms which do not produce a limy skeleton being 

 notably absent from these regions. In their living 

 condition on the reefs the polypes themselves, as 

 well as the skeleton with its organic covering, are all 

 coloured, often with the brightest of tints. Further, 

 it seems to be relatively rare for the whole colony to 

 be of one tint. Sometimes the polypes are sharply 

 contrasted in colour with the coral, sometimes the 

 youngest portions of the colony differ entirely in 

 colour from the older ; while in those forms in which 

 the individual polypes attain a considerable size, the 

 tentacles may be banded or tipped with a colour 

 quite different from the ordinary ground - colour. 

 According to Dr. Hickson (A Naturalist in N. 

 Celebes, London, 1889) the commonest tint is a deep 

 greenish-brown, and next to that, and especially in 

 the younger parts, a bright green. Again, a study 

 of the descriptions and plates in Mr. Saville 

 Kent's great book on the Barrier Reef of Australia 

 shows that after these come shades of red, pink, and 

 yellow, and more rarely electric blue. According to 

 Saville Kent there is great and striking variation 

 in tint both within the limits of a species and even 

 during the course of the life -history of a single 

 colony. 



