114 CORAL AND ATOLLS 



until they arrive at a stage at which they themselves give oft 

 lateral buds. The number of these enlarged lateral zooids 

 may be very great, but not all of them ever attain the dignity 

 of actual branch formation. 



By the end of a hundred days after the receipt of injury 

 the uninjured central end of a branch is roughened all over its 

 surface by the projections of lateral zooids, and those of them 

 that will form new branches have already begun to develop 

 secondary buds from their sides. This process cannot be 

 spoken of with absolute accuracy as an actual repair, for the 

 part injured surely dies, and its substance is never regenerated ; 

 but it is a process by which the sympathetic activity of the 

 remaining zooids in the community is called into action, and 

 the potential power of branch formation inherently lodged in 

 the dominant lateral zooids is turned into a real power. The 

 value of this process in the life-saving of a species is obvious, 

 for the growth tendency of a Madrepora colony is to steadily 

 develop upwards, and the limit of this upward growth is either 

 at the water-level, or at a level at which protection from 

 rough water and moving fragments afforded by the shelter 

 of surrounding rocks is lost. Now a colony which grows up 

 beyond its upward limit of safety will sooner or later have its 

 terminal ramifications killed by exposure, or broken by waves 

 or moving fragments. The injury that destroys the power 

 of the apical zooid causes the lateral buds to branch out at 

 angles to the parent stem, and spread fresh zooid-bearing 

 surfaces far and wide in the area of safety. It is this process 

 that is the great determining cause of the general growth 

 tendency of Madrepora colonies, and the one that causes the 

 deep-water and shallow-water forms of the same species to 

 vary in their vegetative forms of growth. 



3. If in a colony the injury is such that the apical zooid 

 is neither injured nor destroyed, but the damage is limited to 

 the surfaces of a branch, then the repair takes place as in 

 colonies in which every zooid is of equal value. 



This repair is well seen after experimentally inflicted 

 injuries, and the process of carrying out the regeneration of 



