288 Dwellers of the Sea and Shore 



not progress on any such scale as this. For although 

 they are called reef builders they do not in any way 

 erect a permanent structure as living animals; it is their 

 skeletons, compacted in solid masses, but containing 

 material wrought by other agencies as well, that make 

 the reef. And it is very probable that the accretions do 

 not cause it to rise more than an inch in twenty years. 



One of the factors causing the solidification of a reef 

 is the work of the horde of other organisms which 

 inhabit it. Such animals as crabs, moUusks, and sea 

 urchins reduce and perforate the coral by scraping and 

 boring and so weaken It that It breaks away In frag- 

 ments ; these are In turn ground to sand by the continual 

 washing of the waves, thus filling the interstices of the 

 reef. Many wonderful fishes and other creatures, 

 garbed in brilliant tints, make their homes in these 

 stony forests, and the picture they present In the clear 

 blue water of the quiet lagoons, poised among the 

 branches, is one of the rarest offerings of nature. 

 Occasionally one of the branches will have a group of 

 large polyps, each half an inch across, the whole 

 resembling a spike of pretty flowers. The colors of 

 the corals, too, are various and pleasing. Some have 

 red, white, or green polyps on branches of red or of 

 brown. Others may have their whole mass tinted pink 

 or lemon or bright blue. 



Often in the same waters with the reef builders, grow 

 live corals of another type so different In appearance 

 and structure that few persons would be likely to take 

 them for corals. These are the sea fans and the sea 

 pens and the curious organ-pipe corals. They do not 

 always solely secrete lime like the madrepores {i.e., 



