272 THE OCEAN. 



snails, and some were not unlike lobsters or prawns 

 in shape, but soft, and not above two inches long."* 

 Some of the animals thus described by the Captain, 

 were doubtless intruders that had sought shelter or 

 food in the interstices of the coral : the true archi- 

 tects of these wonderful structures are polypes of 

 minute size, which, though of many varying species, 

 and even genera, agree in the simplicity of their form 

 and structure. They consist of a little oblong bag 

 of jelly, closed at one end, but having the other 

 extremity open, and surrounded by tentacles, usually 

 six or eight in number, set like the rays of a star. 

 Multitudes of these tiny creatures are associated in 

 the secretion of a common eton}' skeleton, the coral, 

 or madrepore ; in the minute orifices of which they 

 reside, protruding their mouths and tentacles when 

 under water, but withdrawing themselves by sudden 

 contraction into their holes the moment they are 

 molested. 



It was for a long time supposed that all the islands 

 of coral formation were reared from their bases, 

 fathomless depths in the Ocean, by the unaided efforts 

 of these minute creatures; and from exaggerated 

 notions of the rapidity with which the process was 

 going on, anticipations were frequently uttered that 

 a large portion of the Pacific might, at no very dis- 

 tant period, be occupied by the spreading structures 

 united into a vast coral continent. More accurate 

 observations have, however, satisfactorily proved that 

 the living animals cannot exist at a greater depth 

 than twenty or thirty fathoms, so that the whole of 



* Voyage to Loo-Choo, p. 75. (Constable's edit.) 



