106 CORAL AND ATOLLS 



of tlie manner in which the, by no means satisfactory, classifi- 

 cation of the types affects the phenomena. 



I. Among the colonial forms there is a sympathy of individuals, 

 so that each member of a colony takes its share in resenting 

 the injury to a part, and by an increased activity tends to 

 compensate for its loss, or to assist in its repair. 



In connection with this sharing of each individual in the 

 fortunes of its fellows and of the entire colony, it may be 

 remembered that it was stated that the whole population of a 

 colony may suffer shock from an injury inflicted upon only a 

 small portion of it. Even the zooids remote from the seat of 

 injury will frequently not re-expand for forty-eight hours after 

 the injury was inflicted, and this is so even when the injury 

 is very trivial. 



Now after the receipt of an injury, the effect produced 

 by this communal sympathy varies in different forms of coral, 

 for in a colony, as we have seen, all the members may be of 

 equal importance, or some may be of greater value than others 

 as producers and directors of growth. 



(A) In a coral such as the massive forms of Porites, where 

 the growth-tendency is to form spherical masses, every living 

 entity in the whole vast crowd of active members bears an 

 equal share in building and in reproducing. It is this equality 

 of all the zooids in the community which produces the charac- 

 teristic spherical form of the young growth ; and the equality 

 of the zooids, plus the receipt of injury, produces the typical 

 flat-topped circular rocks into which the old colony generally 

 shapes itself. When a mass of Porites has attained some size 

 as a sphere, the zooids which lie below are necessarily stamped 

 out of existence by the weight of the accumulated mass. It 

 is not often, of course, that the environment is so ideal that 

 anything like a perfect sphere is ever formed, but still, in 

 sheltered pools, many forms of corals may be obtained resting 

 free on the bottom, with every portion of their surfaces living. 



