LIFE AT AND NEAR SURFACE 141 



worms known as "Serpulae," although corals 

 are usually found in large numbers among 

 them. The animals grow thickly upon the 

 wave-washed rocks between high and low- 

 water mark and their hard shells and constant 

 growth protect the outer surface of the rocks 

 from the action of the seas which constantly 

 dash against them. The falling spray and 

 water soon wear away the unprotected top 

 of the rock, however, and in time leave only 

 a narrow rim, covered with the growth of 

 serpula and coral, which then appears exactly 

 like a true atoll in miniature. These little 

 atolls are very common in Bermuda and are 

 known locally as '^Boilers," from the fact that 

 the surf constantly breaks or boils upon them. 



Reef-building corals can live only in warm 

 waters and so coral islands are never seen in 

 the north, the most northern of all living 

 coral-reefs being those of Bermuda. 



Although these wonderful forms of marine 

 life are confined to warm seas, yet we must 

 not think that the arctic and antarctic waters 

 are devoid of animal life in shallow water. 

 The polar seas fairly swarm with marine crea- 



