DEATH-PROCESSES OF CORAL COLONY 131 



factors in atoll formation is great, but it is not as destroyers 

 of living coral that they fulfil their role, for the coral that they 

 take in at their mouths is already dead. 



From the study of the life of the colony in different 

 surroundings, and from the repair of injury, and death, in 

 unsuitable habitats, I think it will be seen that the number 

 of the true species of corals is by no means so great as is at 

 present supposed. There is no doubt that a great number of 

 our museum-made species are mere vegetative varieties, pro- 

 duced in response to the demands of the environment. I 

 do not think it is possible to determine from a fragment of 

 growth — often with no sufficient data — if it be a new species, 

 or even a new genus, or if it be a mere vegetative variety of 

 some already well-known species. There can be but little 

 utility in the naming and describing, with great minuteness, of 

 all these variations ; for of this work there can be no end, and 

 persistent collecting, from even such a small area as the Cocos- 

 Keeling atoll, would yield such a variety of fragments as would 

 occupy a lifetime to describe. In very many cases one single 

 colony could be found to provide several types of growth, which, 

 if presented as fragments, would be deemed to merit individual 

 description as species. In such cases some factor in the 

 physical condition of the surroundings will show, when the 

 colony is in situ, the cause of these different modes of growth ; 

 but when the colony is transported to a museum, it presents a 

 very striking puzzle. 



One side of a colony may be shaded from light, sheltered 

 from currents, or protected from silt ; whilst the other side 

 may be exposed to all these influences : and then it is but 

 natural that the two sides should vary, and — knowing the 

 wonderful plasticity of the zooids — the great differences are 

 not astonishing. 



Besides the occurrence of colonies which exhibit two or three 

 well-marked types of growth, there are those that can only be 

 called " undecided " forms, and these present growths that are 

 intermediate in character between two well-marked and very 

 diverse types. Such " undecided " forms are very common, 



