POLYPS. 



SECTION III. 



THE CLASS OF POLYPI, OR POLYPS. 



THE Class of Polyps embraces radiates which have a 

 tubular or sack-like body, with a circular summit or disk, 

 in the centre of which is an opening popularly called the 

 mouth, surrounded by one or more rows of tentacles ; and 

 which have the interior of the body, except the main 

 central cavity, divided into vertical chambers by vertical 

 plates or partitions, extending from the inner wall to the 

 main cavity, for the whole height of the body. The mouth 

 leads directly into an interior central sac, which is the 

 stomach, and which opens at the bottom into the main 

 cavity. From the main cavity there is free communica- 

 tion with all the radiating chambers, and from the latter 

 free communication through the hollow tentacles which 

 crown the summit. The chambers also communicate with 

 each other by circular openings near the top. Polyps 

 are all marine, and, according to the kinds, are free or 

 attached, single or associated, often in numbers that defy 

 computation. They increase by means of eggs, by budding 

 in a manner analogous to that 

 of trees and shrubs, and by di- 

 vision and subdivision ; so that 

 the largest communities arise 

 from a single parent. Polyps 

 readily reproduce a lost part. 

 Even if cut in pieces, each 

 considerable fragment will, in 

 some cases, become a new ani- 

 mal. With few exceptions, 

 Polyps do not flourish at depths 

 greater than twenty or thirty Pol yp> 



fathoms, and they abound in comparatively shallow wa- 



