90 VORALS AND CORAL ISLANDS. 
In the Corallide, the axis is wholly calcareous, and firm and 
solid throughout, with usually a red color, varying from crim- 
son to rose-red. Here belongs the Coralliwm rubrum, or pre- 
cious coral. The polyp-crust or cortex, which covers the red 
axis or coral, is thin, and contains comparatively few calcare- 
ous spicules, and consequently it readily disappears when the 
dried specimens are handled. In an uninjured state, the polyp 
centres may be distinguished over it by a faint six-rayed star. 
A branch from a specimen obtained by the author at Naples, 
is represented, of natural size, in the cut on page 89. The pol- 
yps, as the enlarged view, by Lacaze Duthiers, shows, are sim- 
ilar to those of other Alcyonoids—the tentacles being eight in 
number and fringed. The figure represents the extremity of 
a branch, magnified about four times lineally, with one polyp 
fully expanded, two partly, and the rest unexpanded. In the 
living Corallium, they open out thickly over the branches, and 
make it an exceedingly beautiful object. The coral grows in 
branching forms, spreading its branches nearly in a plane; and 
sometimes the little shrub is over a foot in height. The au- 
thor just mentioned states that, among the polyps, those of the 
same branch are often all of one sex alone, and that, besides 
males and females, there are a few that combine both sexes. 
The red caleareons axis consists really of united spicules. 
The precious coral is gathered from the rocky bottom of 
the borders of the Mediterranean, or its islands, and most 
abundantly at depths of 25 to 50 feet, though occurring 
also even down to 1,000 feet. There are important fisheries 
on the coast of southern Italy ; of the island of Ponza, off the 
Gulf of Gaeta; of Sicily, especially at Trapani, its western ex- 
tremity ; of Corsica and Sardinia, in the straits of Bonifacio ; 
of Algeria, south of Sardinia, near Bona, Oran, and other 
places, which in 1853 afforded 80,000 pounds of coral; and on 
