Corals and coral islands.

60

CORALS AND CORAL ISLANDS.

Zoothome. -The compound animal mass produced by budding.
Corallum. -The coral either of the compound mass, or of the solitary
polyp.
Corallet (In Latin, corallulum). - The coral of a single polyp in a compound corallum.
Calicle. - The polyp cell in the top of a corallet, or of a solitary
corallum, within the walls of the cells; it is sometimes flat at top, that is,
without the usual depression.
Septa. -The radiated plates of the cell or calicle.
Dissepiments. - Small cross plates between adjoining septa, approximately horizontal; sometimes wanting.
Synapticulce.- Calcareous bars extending across the interseptal spaces,
or loculi, and so uniting the surfaces of adjoining septa.
Tabulce. -Horizontal plates dividing the interior of a cell into a
series of chambers, as in the ancient Favosites, and in the Pocillipoi'.
Tabulate. - Iaving tabulh?. The Tabulatt include the Favosites and
some other ancient corals.
Columella. - The prominent axis of a corallet projecting at the centre
of a calicle. It is generally absent.
Coste. - The vertical ridges over the exterior of some corals; they
usually correspond to the septai, and arc an external extension of them;
but in other cases they are opposite the intermediate chambers, or are
interseptal loculi, as they are often called.
Coenenchyma. -The common mass of the corallum between its different polyp cells or corallets, as in the Madreporae, Gemmiporwa, and
Dendrophylliae.
Epitheca. - The coral layer sometimes deposited over the exterior of
the corallum during the life of the polyp by the outer skin before it dries
away, as explained on page 44.
Peritheca. - The epitheca of a compound group or zo6thome (fig. p. 71).
Exotheca. -- The portion of the corallum outside of the walls of cells
in many coralla of the Astrrea family, and some others. in which the polyps
of the mass are properly in contact, and there is consequently no true
coenenchyma.
Endotheca. -The portion of the corallum inside of the walls of the
cell.
We may now state briefly the characteristics of the
grander divisions of the Actinoid polyps, several of which
have been illustrated in the preceding figures.