POLYPS. SI/ 



SECTION III. 



THE CLASS OF POLYPI, OR POLYPS. 



THE Class of Polyps embraces all radiates which have 

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

 disk, in the centre of which is an opening called the 

 mouth, and around the mouth one or more rows of ten- 

 tacles. The mouth opens directly into an inner sack, 

 which is the stomach, and the stomach opens at the bot- 

 tom into the interior of the body. The interior of the 

 body is divided into vertical chambers by vertical plates 

 or partitions. Through the opening at the bottom of 

 the stomach there is free passage for water, bearing food, 

 into all the chambers, and from one chamber to an- 

 other through a circular opening in the partitions 

 near their top, and from the chambers through the 

 hollow tentacles which crown the summit. Polyps live 

 only in the sea, the so-called fresh-water polyps being 

 acalephs, and, according to the kinds, they 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 Fig. 50 6. 



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 Pobr, Bunodes steiia, Vemii. 



fathoms, and they abound in comparatively shallow wa- 



