158 CORAL AND ATOLLS 



lagoon are described, as well as those of all the intermediate 

 situations ; and the idea remains that a species is either a reef 

 coral or a lagoon coral. Now it is as well to say at once that 

 the distribution of the corals of this atoll does not follow any 

 such hard and fast lines. There are several species which are 

 always more abundant on the barrier, but they are also to be 

 found in the lagoon, just as are the more typical lagoon 

 corals to be found on the barrier. The essential feature in 

 the distribution of atoll corals is that it is a distribution of 

 types, and not of species ; the barrier types are not species but 

 are the barrier forms of lagoon species, and vice versa. The 

 subject of the modification of the corals is an interesting one, 

 and must force itself on the collector as he gains experience ; 

 for as he first makes his collections from the lagoon and the 

 barrier he begins to believe that the number of species is 

 without end, and it is not till he has spent some time in this 

 pursuit that he comes to realise that the species are in reality 

 few, but the adaptations of the corals to their environment 

 are legion. The student of corals who should see these col- 

 lections only when far from their site of growth would be 

 entirely without a clue to account for the endless range of 

 forms which any casual visitor to an atoll might collect. There 

 are many factors which tend to modify the outward form of a 

 coral's growth, and to confuse any one who, without a know- 

 ledge of their habitat, would attempt their classification. This 

 point has been studied in connection with the corals them- 

 selves. When distribution is spoken of here, it is this dis- 

 tribution of types that is meant, a very different thing from a 

 distribution of separable species. 



It has been said, and much weight has been given to the 

 assertion, that the nearer to the edge of the barrier one goes, 

 the more luxuriant becomes the coral growth. In this atoll, at 

 any rate, this is definitely not the case ; and any arguments 

 for the formation of the atoll based on this assumption cannot 

 be valid. It is not necessary to assume that corals flourish best 

 in the surf-line because of the better aeration, or that they 

 receive a more abundant supply of food, and so grow better ; for 



