FORM AND 8TRUCTURE. 



467 



Polyps arc marine radiates which have a sack-like or 



tubular body, with a circular top or disk, in the center of 



FlG 704 which is an opening 



called the mouth ; 

 and surrounding the 

 mouth are one or 

 more rows of hollow 

 feelers or tentacles. 



The mouth opens 

 directly into an inner 

 sack, which is the 

 stomach, and this 

 stomach opens at the 

 bottom into the main 

 cavity of the body. 



The main cavity 



Qf ^ bo( j y . g diyid _ 



ed by radiating septa or partitions, which run from the 



FIG. 705.* 



Cluster of Coral-Polyps, Asteroides calycularis, 

 M. Edwards in various stages of expansion. 



Cross section of a Polyp, showing the Septa. 



bottom to the top, and from the outer wall to the stomach. 

 These radiating partitions are in pairs, and the number of 



* Figs. 668, 700, 705, 706, 707, 713, 721, and 730, are from Dana's splendid "Coral 

 aud Coral Islands." 



