42 CORALS AND CORAL ISLANDS. 
Il. 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 Actinie. 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- 























CARYOPHYLLIA 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) 
