42 



CORALS AND CORAL ISLANDS. 



II. CORAL-MAKING ACTLNOID POLYPS. 



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

 €ells, food, digestion and respiration of the coral-making polyps 

 here included, nothing need here be said, these characters being 

 the same as in the Actiniae. Their more striking peculiarities 

 depend on the secretion of coral, making them fixed species, 

 and involving an absence of the base ; and, in the 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 corallum. These secretions take place among the tis- 



CARYOPHYLMA CYATHUS. 



sues 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, 

 from the Mediterranean, the upper extremity is a depression, 

 or calicle, enclosed by a series of radiating calcareous (coral) 



