54 The Under-Water World 



from the main stems. When brought 

 ashore the outer crust, or bark, constitu- 

 ting the most recent growth, filled with 

 living polyps, is brushed off, the outer 

 portion of the skeleton filed away, and 

 the inner core polished with oil, and 

 finally with steel. The commercial value 

 varies according to the condition of the 

 growth before being worked, the corals 

 suffering much from boring sponges, 

 worms and molluscs. The world-famed 

 Reef-Building Corals, which form large 

 groups of islands in shallow waters, are 

 the result of long continued budding on 

 the part of the polyps, whose stony 

 castles pile one upon another as each 

 short-lived generation gives place to the 

 new one that follows after. Despite the 

 depredations of burrowing animals, and 

 such fish as the parrot wrasses and coffer 

 fishes that literally browse upon living 

 coral with their chisel-shaped teeth, the 

 polyps multiply so fast as to more than 



