ON CORAL AND CORAL REEFS 119 



has made us very completely acquainted with the struc- 

 ture and habits of all these polypes. We know that, 

 among the sea-anemones and coral-forming animals, 

 each poylpe has a mouth leading to a stomach, which 

 is open at its 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 per- 

 form 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 incomplete divisions, give rise 

 to a sort of sheet, or turf, formed by innumerable con- 

 nected, and yet independent, descendants. 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, sometimes of very con- 

 siderable 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 support- 

 ing stem. It is a sort of natural cooperative 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 impreg- 



