912 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 stony 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 tirne 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.) 
