CORAL BUILDERS. 243 



nexion with the ground, and even penetrating far 

 into the living portion of these compact communities. 

 The number of these boring animals is quite in- 

 credible, and they belong to different families of the 

 animal kingdom; among the most active and powerful 

 we would mention the date-fish, and many worms, of 

 which the Serpula is the largest and most destructive, 

 inasmuch as it extends constantly through the living 

 part of the coral stems. On the loose basis of a 

 brain coral (Meandrina), measuring less than two feet 

 in diameter, we have counted not less than fifty holes 

 of the date-fish some large enough to admit a finger 

 beside hundreds of small ones made by worms. 

 But however efficient these boring animals may be, 

 in preparing the coral stems for decay, there is yet 

 another agent, perhaps still more destructive, we 

 allude to the minute boring-sponges, which penetrate 

 them in all directions, until they appear at last com- 

 pletely rotten through." l Yet the coral animals would 

 seem to contribute themselves a little protection from 

 their enemies, for in some of the species the lower 

 edge of the dying polyps secrete an outer layer of 

 denser, and more impervious, material over the dead 

 coral stem, and, besides this, the older polyps before 

 death increase their coral secretions within, so as to 

 fill up gradually the pores of the coral, as their own 



1 Agassiz. Coast Survey Report for 1851. 

 R 2 



