vi.] ON CORAL AND CORAL REEFS. 115 



inner end, and thus communicates freely with the general 

 cavity of the body ; that the tentacles placed round the 

 mouth are hollow, and that they perform the part of 

 arms in seizing and capturing prey. It is known that 

 many of these creatures are capable of being multiplied 

 by artificial division, the divided halves growing, after a 

 time, into complete and separate animals ; and that many 

 are able to perform a very similar process naturally, in 

 such a manner that one polype may, by repeated incom- 

 plete divisions, give rise to a sort of sheet, or turf, formed 

 by innumerable connected, and yet independent, descen- 

 dants. Or, what is still more common, a polype may 

 throw out buds, which are converted into polypes, or 

 branches bearing polypes, until a tree-like mass, some- 

 times of very considerable size, is formed. 



This is what happens in the case of the red coral of 

 commerce. A minute polype, fixed to the rocky bottom 

 of the deep sea, grows up into a branched trunk. The 

 end of every branch and twig is terminated by a polype ; 

 and all the polypes are connected together by a fleshy 

 substance, traversed by innumerable canals which place 

 each polype in communication with every other, and 

 carry nourishment to the substance of the supporting 

 stem. It is a sort of natural co-operative store, every 

 polype helping the whole, at the same time as it helps 

 itself. The interior of the stem, like that of the branches, 

 is solidified by the deposition of carbonate of lime in its 

 tissue, somewhat in the same fashion as our own bones- 

 are formed of animal matter impregnated with lime salts ; 

 and it is this dense skeleton (usually turned deep red by 

 a peculiar colouring matter) cleared of the soft animal 

 investment, as the heart-wood of a tree might be stripped 

 of its bark, which is the red coral. 



In the case of the red coral, the hard skeleton belongs 

 to the interior of the stem and branches only ; but, in 



I 2 



