96 CORALS AND CORAL ISLANDS. 



alive over the whole surface, owing to a symmetrical and un- 

 limited mode of budding, are nothing but lifeless coral 

 throughout the interior. Could the living portion be sepa- 

 rated, it would form a hemispherical shell of polyps, in most 

 species about half an inch thick. In some Porites of the same 

 size, the whole mass is lifeless, excepting the exterior for a 

 sixth of an inch in depth. 



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

 to the growth of zoophytes. The rising column may increase 

 upward indefinitely, until it reaches the surface of the sea, and 

 then death will ensue simply from exposure, and not from any 

 failure in its powers of life. The huge domes may enlarge till 

 the exposure just mentioned causes the death of the summit, 

 and leaves only the sides to grow, and these may still widen, 

 it may be indefinitely. Moreover, it is evident that if the 

 land supporting the coral domes and trees were gradually 

 sinking, the upward increase might go on without limit. 



In the following of death after life " gequo pede," there is 

 obedience to the universal law. And yet the polyps, through 

 this ever yielding a little by piecemeal, seem to get the better 

 of the law, and in some instances secure for themselves almost 

 perpetual youth, or at least a very great age. Of the polyps 

 over an Astrsea hemisphere, none ever die as long as the dome 

 is in a condition of growth ; and the first budding individual, 

 or at least its mouth and stomach, is among the tens of 

 thousands that constitute the living exterior of the dome of 

 fifteen feet diameter. In the Madrepore, the terminal parent- 

 polyp of a branch grows on without being reached by the 

 death-warrant that takes off at last the commoners about the 

 base of the tree ; it keeps growing and budding, and the tree 

 thus continues its increase. 



The death of the polyps about the base of a coral tree 



