72 NATURAL HISTORY. [n. ZOOL. GAL. 
(Cases 24 to 26). The axes of some of these kinds have 
been called, from their colour, Black Coral , and were for¬ 
merly much esteemed for their supposed magical and 
medical qualities. They are now chiefly used to make 
riding whips and whisks. 
In some genera a large quantity of calcareous matter is 
deposited along with the horny matter, forming a stone¬ 
like axis, as in the Red Coral, Cor allium (Case 21); and in 
other kinds the calcareous matter is only deposited in 
certain parts of the axis, leaving the rest simply formed 
of the horny animal matter as in the genus Isis (Case 
21). In this kind the axis has been considered as jointed, 
because the stony and the horny parts easily separate 
from each other when the mass of the animal has been 
removed and the axis is dried; but a larger and larger 
quantity of stony matter is gradually deposited as the 
mass increases in size, and in the large masses, the axis 
of the lower part is almost entirely stony, like the axis of 
Corallium. Specimens shewing all the changes are in the 
collection (Case 21). Lamarck, not being aware of this 
change, considered the axis of the old specimens as a 
different genus. The Antipathes (Case 27) have the same 
kind of animal and axis as the Gorgonia, but the skin of 
the animal is thin, cellular, and easily leaves the axis 
bare, when the mass is taken out of the water. 
In the genus Hyalonema , (Case 28,) the animal mass, 
instead of forming a single axis for its support, secretes in 
the middle of its substance a bundle of thin transparent 
fibres, looking exactly like a rope of spun glass; each of 
these fibres is formed of numerous concentric coats, like 
the axis of Gorgonia , and they are each of them enlarged 
in size by a new layer of mineral matter, secreted by the 
thin membranes which surround each of them, as the 
mass requires more support. Unlike the axis of Gor¬ 
gonia, the fibres are formed of nearly pure flint, and are 
hard enough to scratch glass, and the mass, instead of 
forming for itself an expanded base, lives with the end of 
the axis sunk in a species of sponge. This genus is found 
in the Japanese seas. It is the only one, whose animal 
nature is well determined, that secretes pure silex, for the 
Tethya probably belongs to the vegetable kingdom. 
The Sea Pens, Pennatulidce , (Case 28,) have many 
characters in common with the Gorgonice. They have 
