52 ANTHOZOA. 



is built (Fig. 35). During the life of the Madrepore, 

 every one of these minute cells gave issue or concealment 



FlG. 35. ORIFICE OF MADREPORE. 



to a radiant Polype, which, like a living flower, protruded 

 its eight arms in search of food. 



In the hot climates where these stone-making corals 

 abound, they frequent shallow bays and sheltered spots, 

 where they can enjoy the full influences of light and are 

 unexposed to the agitation of the ocean : in such situa- 

 tions the submarine rocks become gradually incrusted 

 with their calcareous skeletons, and if left undisturbed, in 

 the lapse of years successive generations deposit such 

 large quantities of calcareous matter as to form beds of 

 considerable thickness. 



In the formation of their massive skeletons, it must be 

 remembered that life and death constantly keep pace with 

 each other. The living mass, whilst growing at the top, 

 is with concurrent progress perishing beneath, leaving 

 the imperishable stone a still accumulating mound. With 

 such a mode of increase, there is no necessary limit to 

 the growth of these zoophytes. The rising mass may 

 expand upwards, until it nears the surface of the sea, 

 when death ensues simply from exposure, and not from 

 any failure in its powers of life ; still growing round the 

 margin of the rock itself has formed, it spreads on every 

 " side. Old ocean raves to see a whole domain thus res- 

 cued from his grasp, and piles upon the nascent island 

 mud and weeds, which soon produce a vegetable soil; 

 seeds brought by birds, and cocoa-palms take root upon 

 the new-born surface, soon thick groves appear, inviting 

 human occupation, and man comes at last to take posses- 

 sion of a territory reared by the unaided efforts of these 

 humble creatures. 



