254 CCFXENTERATES : POLYPS. 



Polyps increase by means of eggs, by budding in a 

 manner much like that of trees and shrubs, and by 

 division of one animal into two or more, so that the 

 largest communities arise from a single animal. The 

 eggs are formed on the vertical partitions, and pass 

 out, through the mouth, into the water. When first 

 hatched, the young do not look like the parent, but are 

 little oval bodies which move freely about by means of 

 the fringe-like appendages, called vibratile cilia, with 

 which they are covered. At length each becomes 

 attached to a rock, shell, or seaweed, and soon assumes 

 the form of the parent. If it is a kind which buds, 

 there soon grow from its sides or base others exactly 

 like itself, and from these, in turn, bud other polyps 

 of the same kind. Thus the community goes on grow- 

 ing till it has reached its limits of increase. If it is a 

 kind which increases by division, it widens as it grows 

 upward, the walls in two opposite places begin to ap- 

 proach each other, and soon the polyp is divided into 

 two, with two mouths and two circular disks surrounded 

 by tentacles, instead of one as before the division. 

 The polyps thus formed divide in the same way, and 

 this process is continued till from a single polyp there 

 is formed a large and beautiful cluster. 



Polyps readily reproduce lost parts, and even if cut 

 in pieces, each fragment will, in some cases, become 

 a perfect animal. Polyps vary in size from extreme 

 minuteness to those that are more than a foot across. 

 Some, like the Sea Anemones, Figure 486, are wholly 

 soft ; others secrete a more or less solid framework, 

 which is called coral ; and those which secrete coral 

 are called Coral Polyps, or Coral Animals. Some per- 

 sons suppose that coral is something that is built by 



