116 CORAL AND ATOLLS 



an injiiry, a remarkable state of things is brought about, which 

 may be stated as follows : 



II. A coral may repair an injury hy a new groioth of a different 

 type from that of the colony, and in such cases the repair 

 groioth is of a form better suited to the environment than is 

 the form of the parent colony. 



It must be borne in mind that the physical conditions of 

 the atoll are not absolutely constant. Seasonal changes in sets 

 and strength of currents are perpetually causing alterations at 

 all points of the island ring, and a habitat may alter greatly in 

 its physical conditions in the course of a few months. When 

 a coral embryo settles down upon a basis, and starts the 

 founding of a colony, the type of growth which will result will 

 be that best fitted to the environment as the embryo finds 

 it. But suppose that, after the founding and growth of a 

 colony, the physical conditions of the environment change ; 

 rouofh water is admitted, silt settles down, or the water 

 becomes shallow and calm : then the growth of the colony 

 may not be the ideal one for flourishing under these new 

 conditions. 



In many places where the conditions are prone to vary, 

 the habitat of the corals may alter in its physical nature in 

 more or less regular cycles. Where, as at the eastern 

 extremity of Pulu Tikus, a spit runs out, building sheltered 

 pools and protecting the shore for a considerable distance, and 

 then later on, in the periodical cycle of currents and eddies, 

 is carried* away, many corals must be subjected to a great 

 variation of environment. In such circumstances no doubt 

 many colonies die, for, as we have seen, a sudden change of 

 habitat cannot be resisted when a form is well adapted for one 

 definite kind of environment, and in any case the colonies 

 are liable to injury and partial death in their changed 

 surroundings. 



When such injury falls on a coral not ideally situated, 

 the repairing growth exhibits a strange independence, and, 



