COEAL. 



471 



thus the community goes on growing till it has reached 

 its limits of increase. If it be a kind which increases by 

 division, it widens as it grows upward, and soon there 

 are two months instead of one ; and at length the polyp is 

 divided into two, so that there are two mouths, and two 

 circular disks surrounded by tentacles, instead of one as 

 before the division ; and 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, in some cases, will become a per- 

 fect animal. 



Polyps vary in size from extreme minuteness to those 

 that are more than a foot in diameter. Some kinds, as 

 the Sea-anemones (Fig. 702), are wholly soft ; others secrete 

 a more or less solid framework, called coral or corallum. 



Some people suppose that coral is built by an insect, as 

 the bee builds comb, or the wasp its nest ; and the indus- 

 try of this supposed insect is often spoken of. But it is 

 not proper to give the name in-' 

 sect to the Coral-polyps, for 

 they are in no way related to 

 insects, either in appearance, 

 structure, or habits. Coral is 

 not something which is built, 

 but something which grows. It 

 is the skeleton, or many united 

 skeletons, of polyps / and these 

 animals exhibit no industry in 

 forming it, any more than do 

 other animals in forming their own bones. Coral is 

 not a house in which the animal lives; on the contrary, 

 the coral is wholly inside of the animals, and it is only 



FIG. 708. 



Coral, Asteroides calycularis, Milne- 

 Edwards. The Coral of Fig. 704. 



