CCELENTERATA 77 



resembling the Actinia in structure. 11 The skeleton of 

 a single polyp (called corallite, Fig. 292) is a copy of 

 the animal, except the stomach and tentacles, the earthy 

 matter being secreted within the outer wall and between 

 each pair of partitions. So that a corallite is a short 

 tube with vertical septa radiating toward the center. 12 



FIG. 28. Madrepora aspera, living and expanded ; natural size. Pacific. 







A sclerobasic coral is a true exoskeleton, and is dis- 

 tinguished by being smooth and solid. The polyps, 

 having eight fringed tenacles, are situated on the out- 

 side of this as a common axis, and are connected to- 

 gether by the fleshy ccenosarc covering the coral. 



(i) Sclerodermic Corals. ' Astrcea is a hemispherical mass 

 covered with large cells. Meandrina, or "brain coral," 



