1907.] AND SUPPOSED SPECIES IN CORALS. 535 



and striking coloui', and yet the corals are identical wlien dead, 

 and the zooid in both cases is the same, 



Montipores vaiy from yellow to olive-green and brown, and yet 

 the zooid is always of the same sulphur-yellow, and the coral is 

 always identical in other respects. 



The general coloration of the coral body cannot therefore be 

 regarded as specific, and the coloration of the zooids also shows a 

 sti-ange inconstancy. Although as a rule the zooids of different 

 colonies of identical species — though the colonies may be very 

 different in appeaiunce — ai'e similar, yet in one colony the 

 individual zooids may be very variously coloured. 



There is one very striking case, that is not uncommon in the 

 atoll, of an Astrea, where the zooids on the upper surface are a 

 line fluorescent green, at the sides of the growth brown, and 

 below white. And here it would appear- — as also probably in 

 the deeper water forms — that light had some influence on the 

 production of the jjigments. Despite this peculiar variation 

 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 

 sti'ange growth-forms and abnormal coloration of Pocillopora the 

 zooid remains constantly brown ; and in Montipora., constantly 

 pale sulphur-yellow. In Stylophora, whether the coral is the 

 thinly branched and colourless deep form, or the thickly bi'anched 

 and brownish shallow- water form, the zooid is always of the same 

 yellow colour. 



In considering the vegetative 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 physical conditions 

 of its surroundings are always altering. The terms rough water 

 and smooth water, deep or shallow, and sedimenting or non- 

 sedimenting, are therefore only comparative ; for what to-day is a 

 habitat free from sediment, may in the course of a few weeks 

 Tiecome the site of a copious deposition of silt. The rise and fall 

 of the tide across the barrier must of necessity caiiee great changes 

 in the life svirroundings of the corals in its passage ; and so a 

 colony, found in a calm pool, may for a part of its life be exposed 

 to violent wave action. This must always be borne in mind, for 

 the results obtained by careful collecting will not be pure. Corals 

 may be found of different forms, growing in close proximity ; but 

 far from being evidence that they are different species, and not 

 mere varieties, they demonsti'ate the fact that the physical con- 

 ditions of their surroundings are inconstant, and that, for a cycle 

 each form is, in its turn, the most suitable. 



The very inconstancy of the environment is one factor in 

 showing the plasticity of the corals, for the partial death and 

 repair caused by changed conditions afford striking evidence of 

 the wonderful powei's of varied building possessed by the zooids. 



Experiment with constant physical surroundings must be the 



