252' 



PHYSIOGRAPHY. 



[chap. 



divide and subdivide, the product of each division growing 

 into a perfect polype. By frequent repetition of these 

 processes of budding and spHtting, the corals may form 

 masses of great size ; in some cases, branching like a tree, 

 with separate polypes budding out ia sU directions ; and, in 

 other cases, spreading into a confused mass, like the well 

 known " brain-stone coral," which is to be seen in every 

 museum. Since the multiplication of the polypes may go 

 on to an almost unlimited extent, it is evident that the 



Fig. 72. — Thecopsa>nniia sOiialiSy Pourtales, 



aggregated mass of coral maybe of enormous size, although 

 tlie separate polypes are but small. In fact, it is the growth 

 of coral, in this manner, that forms those masses of land 

 which are known as "coral-reefs" and "coral-islands." 



Such land is popularly said to be " built " by the coral- 

 animals, but it should be understood that it is not a construc- 

 tive work, like the nest of a bird, or the comb of the bee. 

 The land is simply an accumulation of the calcareous re- 

 mains, or skeletons, of the coral-polypes. The formation of 

 this land is, indeed, very much like the formation of the 



