GROWTH OF THE CORAL COLONY 79 



growth tends to become irregular — at different times different 

 portions of the colony have sudden phases of active growth, 

 and these may be due to no observable cause. Again, some 

 zooids of the colony may have special advantages due to the 

 environment, and will grow and divide excessively, in such a 

 manner that they dominate the growth of the whole colony, 

 and consequently modify its form. The conditions of the 



Fig. 18. 



Fig. 19. 



Vegetative E,epkoduction 

 IN Corals. 



Meandrine type of division : no 

 separation of daughter zooids. 



Vegetative Reproduction 

 in Corals. 



Diagram showing an Astrcea 

 assuming (as a sport) a Mean- 

 drine form of division. From 

 an actual specimen. 



environment may call forth special reproductive activity in 

 any portion of the growth, and so in a colony, all of Avhose 

 units are of equal importance, some part will be found to be 

 growing onwards, whilst all the remainder of the zooids are 

 practically at rest. In this way the typical hemisphere of 

 such colonies may become modified as a creeping plate, an 

 encrusting layer, a pseudo-branching form, or a mass of mere 

 irregular nodules. 



Thus, in those corals whose zooids are naturally of equal 

 reproductive importance, forms may arise, as the result of 

 physiological need, that simulate exactly other forms, the re- 

 productive activities of the zooids of which are normally 

 unequal. 



