2i6 CORALS 



and dead ccjials, and supports a rich fauna of lish, Crustacea, 

 starfishes, and holothuria, sea-worms, and smaller inverte- 

 brate organisms, as well as a flora of seaweeds ; but no 

 two reefs seem to be exactly alike, and the complex of 

 natural forces that plays upon them leads to the abundance 

 of some kinds of corals on this reef and to their suppression 

 on that, to the richness and vigour of growing corals in 

 countless masses, or to the accumulation of quantities of 

 dead and decaying lumps of coral among a relatively few 

 surviving living ones. 



The first impression of one coral reef may be that it 

 consists of nothing but huge shrubs of stag's-horn Madre- 

 pores, of another that it is all palmate Madrepores, of a third 

 that it is all Lithothamnion, although a closer examination 

 shows that many other kinds of coral occur among the 

 prevalent forms. In other places, however — and this seems 

 to be the case particularly on the fringing reefs — the corals 

 of different species are more evenly distributed, Madrepores, 

 Porites, Millepores, Seriatopores, and other kinds being all 

 mixed up together in such a way that it is difficult to say 

 that any one species is predominant. 



With such variety in the composition of the living coral 

 reefs, any detailed account that may be given must be 

 regarded as the description of a particular part of a particular 

 reef and must not be considered applicable to the reefs in 

 any other district. It is perhaps one of the greatest charms 

 of coral reef work that it presents so much variety. As 

 the naturalist surveys the fringing reef of a coast, he finds 

 with every mile that he traverses a different grouping of the 

 species of corals ; he discovers new varieties here and there, 

 he sees different kinds of fish and holothurians, he may 

 even find abundance of some species which formerly he 

 thought to be rare. 



And as with the details of composition, so with the general 

 effects. On some reefs he may be charmed with the richness 

 and variety of the colours, on others disappointed with the 

 almost uniform display of dull brown or dirty pink tones. 



Coral reefs also differ very much from one another in 

 what may be called their vigour or vitalitv. In some 



