LIFE-PROCESSES OF CORAL COLONY 109 



factor that calls into existence the flat- topped Poriies colony 

 also fashions the atoll-shaped reef. 



This question Avill therefore be again referred to in the 

 chapter dealing with the formation of reefs. 



The same process which leads to the normal shaping of 



Fig. 39. 



A Small Colony of Arjarida 



To show the death of the upper surface due to the dropping of 

 sediment upon the colony. 



massive coral colonies may be seen on a small scale at myriad 

 points upon the surface of the growth. The actual amount of 

 living tissue in a large growing boulder is very small, for the 

 depth to which the living animal tissues of the zooid extend 

 beneath the surface is very slight, and yet the calcified portion 

 which extends from the living margin to the centre of the rock 

 must in no way be regarded as the accumulated and dead 

 remains of past generations. It is in reality the skeletons 

 of those zooids whose mouths are now showinsf at the surface. 

 It follows, therefore, that since the skeleton devoid of animal 



