144 
NATURAL HISTORY. [NE W BUILDING. 
In general, the common mass has an expanded base 
by which it is attached to some marine body, and when 
the mass is of a low rounded shape, as in Lobularia , (Case 
28,) the spiculse in the substance of the skin are strong 
enough to support the mass, but when the mass assumes 
an erect or a branched tree-like form, the animals secrete 
in the centre of their body a more or less rigid support, 
which has been called their axis, and which has some¬ 
times, though erroneously, (from its being commonly seen 
in collections without the remains of the investing animal,) 
been considered the entire coral. This axis is thickened 
by depositions of fresh layers of horny matter on its 
surface as the mass increases in size and requires more 
support, the increase of the thickness and length of the 
axis being always simultaneous with the growth of the 
mass. In some kinds, the axis is only formed of an im¬ 
mense number of spiculse, like those in the substance of 
the skin, being crowded together in the centre, as in the 
genus Briar eum (Case 28). 
In general it is formed of a quantity of horny matter, 
which is deposited in successive layers, as in Gorgonia 
(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, Corallium (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, notbeing aware of this 
change, considered the axis of the old specimens as a 
