88 



CORAL AND ATOLLS 



habit of growth, and form encrusting layers on the surface of 

 dead massive colonies ; but they are not corals which are at all 

 common in any but the calmest water. Their usual home is 

 the lagoon, and the greatest normal departure from their 

 favourite habitat is in the current-swept shallow inlets to the 

 lagoon ; and here an endless series of modifications may be 



Fig. 23. 



a b c 



Types of Growth of Montipora. 

 a. In barrier pools, h. In deep water, c. In rough water. 



collected, ranging from branching forms to mere amorphous 

 masses and encrusting layers. 



The rough-water forms of the Madrcpora are highly cha- 

 racteristic, and all depend on the processes which always occur 

 in this group when the "dominant apical zooid " is injured. 

 Instead of a growth that consists of few dominant zooids 

 situated at the extremities of long branches, a rounded mass 

 is formed ; and it is composed of little groups of symmetrical 

 zooids surrounded by others that are asymmetrical — each 

 little group representing a branch in an extremely abbreviated 

 form. 



From these extreme rounded masses, with branches that 

 are mere bosses on the general surface, every transition form 



