22 CORALS AND CORAL LSLANDS. 



Each of these characters is evidence of the superior grade of 

 this division of polyps. 



II. CORAL-MAKING ACTINOID POLYPS. 



Of the form, tentacles, mouth, stomach, fleshy septa, lasso- 

 cells, food, digestion and respiration of the coral-making polyps 

 here included, nothing need here be said, these characters 

 being the same as in the Actinise. Their more striking pecu- 

 liarities depend on the secretion of coral, making them fixed 

 species, and involving an absence of the base ; and, in the 



CAKVOPHYLLIA CYATHUS. 



case of the majority of the species, on the extent to which they 

 multiply by buds, in imitation of species in the vegetable 

 kingdom. 



The coral skeleton which the secretions of polyps form is 

 called the coi-allum. These secretions take place among the 

 tissues of the sides and lower part of the polyp, but never in 

 the disk or stomach, as this would interfere with the functions 

 of these organs. In the above sketches of a simple coral, 



