112 CORAL AND ATOLLS 



There is, as Ave have seen, no portion of a Maclrepora 

 colony which normally dies, and the obliteration of animal 

 tissues in the proximal portion of any zooid is a late change. 

 If the fracture takes place not very far from the end of a 

 branch, the inherent vitality of the terminal zooid predomi- 

 nates, and it starts the repair by continuing to grow out in 

 the direction of its original axis of growth, and by budding 

 new zooids from its sides. 



In a measured specimen which was fractured cleanly across 

 one of the main branches without other injury to the colony, 

 the apical zooid had, at the end of a hundred daj's, grown 

 out 1 centimetre and had budded from its sides forty lateral 

 daughter zooids; and the general surface of the fractured end 

 showed seventy newly formed corallites of old and new zooids. 

 During the same interval of time a branch of about the same 

 diameter on the same colony, which had received no injury, had 

 advanced by 1-5 centimetres and had added about a hundred 

 and twenty new lateral zooids ; so that, judged as growth in 

 these corals must be judged, the rate of repair is a rapid one. 

 In this case the dominant zooid is apical, and its superior 

 vitality enables it to regenerate and to continue the growth 

 along the lines of original branching ; but if the vitality of the 

 " dominant apical zooid " is definitely destroyed, a very different 

 state of affairs is brought about. 



2. If the " dominant apical zooid " is destroyed, and 

 especially if the damage is extensive and affects a large area 

 of a branch, the predominant functions of the apical zooid are 

 taken over by the more vigorous lateral zooids, so that there 

 is a tendency towards branch-formation below the site of 

 injury. 



This state of things, when put into terms of the life- 

 functions of the colony, means that potentially almost any 

 lateral bud possesses the inherent vitality of the apical zooid, 

 but it is only in times of stress to the colony that this 

 potential power becomes actual. A stem of a Madrcpora 

 colony may shoot up straight for the distance of a foot, and 

 show nothing more worthy of the name of a branch than the 



