1907.] AND SUPPOSED SPECIES IJS^ CORALS. 539 



tlie general study of the phenomena as they affect the life-history 

 of the coral, than from a survey of the manner in which the, by 

 no means satisfactory, classification of the types affects the 

 phenomena. 



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

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

 the injury to a part, andj hy 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 remem- 

 bered 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, and that even the zooids remote from the seat of 

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

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

 very trivial. 



Now after the receipt of an injuiy, the effect produced by this 

 communal sympathy varies in diffei-ent forms of coral, for in a 

 colony, as we have seen, all the members may be of equal import- 

 ance, or some may be of greater value than others as producei's 

 and directoi'S 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 that produces the characteristic spherical 

 form of the young growth, and the equality of the zooids plus 

 the receipt of injury produce the typical flat-topjDed circular 

 rocks into which the old colony generally shapes itself. When a 

 mass of Porites has attained some size as a sphere, the zooids that 

 lie below are necessai-ily 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. The original nucleus has been covered equally 

 upon all sides, and the weight of the colony is not sufiicient to 

 cause the death of those zooids that happen to live on the under 

 side. But as this mass increases in size and weight, death of the 

 lowest zooids must inevitably occur, and the rest of the surface- 

 area carrying on the compensating building, will cause the growth 

 to become dome-shaped. Theoretically, the dome shape would be 

 the type of form of all the massive species that follow this method 

 of growth and division, but practically the dome shape is far less 

 common than the flat-topped rock, and this is for the reason that 

 injury to the uppermost zooids is usual in the life-history of a 

 colony. 



