84 CORAL FORMATIONS, 
at summit a star of tentacles, constitute the flowering zoophytes of 
coral reefs. 
Those coral animals which do not bud are to all external appear- 
ance true actinie. The existence of coral in the living coral zoophyte 
is nowhere apparent, and would not be suspected if not previously 
known; for, as before stated, it is wholly internal, and the visible 
exterior is the fleshy skin of the polyp. 
c. Secretion of coral.—We have already remarked on the general 
nature of coral secretions. ‘These secretions, it should be further 
observed, increase within simultaneously with growth, and every new 
animal adds to those previously formed. ‘They go on throughout 
the sides and base of each polyp, excepting generally the exterior 
skin, as above stated; and the whole forms a calcareous framework 
penetrated by the animal tissues, some of these tissues corresponding 
to and occupying the cellules of the corallum, and others penetrating 
the solid parts in minute ramifications. Coral is also secreted between 
the radiating fleshy lamelle of the internal cavity of the polyp, pro- 
ducing the radiated calcareous lamelle which constitute the star of a 
cell. In the corallum of a Madrepora or an Astrea each surface cell 
or star belonged to a separate polyp, and the star was formed as here 
explained. 
It would lead to too long a digression from the main topic before us 
to explain the principles upon which the forms of zoophytes depend. 
They are dwelt upon at length in another volume. In this place we 
may briefly allude to the principal varieties of form proceeding from 
the budding process, and to a single point in their mode of growth, 
upon which much of their importance in reef-making depends. 
d. Forms of actinoid zoophytes.—Zoophytes imitate nearly every 
variety of vegetation. ‘T'rees of coral are well known; and although 
not emulating in size the oaks of our forests,—for they do not exceed 
six or eight feet in height,—they are gracefully branched, and the 
whole surface blooms with coral polyps in place of leaves and flowers. 
Shrubbery, tufts of rushes, beds of pinks, and feathery mosses are 
most exactly imitated. Many species spread out in broad leaves or 
folia, and resemble some large-leaved plant just unfolding: when alive 
the surface of each leaf is covered with the polyp flowers. The cactus, 
the lichen clinging to the rock, and the fungus in all its varieties, have 
their representatives as regards external form. Besides these forms 
imitating vegetation, there are gracefully modelled vases, some of 
which are three or four feet in diameter, made up of a network of 
