98 



CORAL AND ATOLLS 



the production of the pigments. Despite this peciihar varia- 

 tion of the colour of the zooids in one colony, it remains a 

 fact that the zooid is the true index of the species. In all the 

 strange growth-forms and abnormal coloration of PocillojJora 

 the zooid remains constantly brown ; and in Montipora, con- 



FiG. 32. 



Colony of Poc'dlopora 



Whose general colour may be either a delicate pink or a yellowish 

 brown. In both cases the zooid is identical and coloured brown. 



stantly pale sulphur-yellow. In Stylo-pora, whether the coral 

 is the thinly branched and colourless deep form, or the thickly 

 branched and brownish shallow- water form, the zooid is always 

 of the same yellow colour. 



In considerinsr the vesretative forms of the corals of an 

 atoll, it must always be remembered that the environment is 

 not a constant one. Although the coral colony is absolutely 

 debarred from changing the site of its growth, still the 



