formed.

This is what happens in the case of the red coral of commerce. A
minute polype, fixed to the rocky bottom of the deep sea, grows up
into a branched trunk. The end of every branch and twig is terminated
by a polype; and all the polypes are connected together by a fleshy
substance, traversed by innumerable canals which place each polype in
communication with every other, and carry nourishment to the substance
of the supporting stem. It is a sort of natural co-operative store,
every polype helping the whole, at the same time as it helps itself.
The interior of the stem, like that of the branches, is solidified
by the deposition of carbonate of lime in its tissue, somewhat in the
same fashion as our own bones are formed of animal matter impregnated
with lime salts; and it is this dense skeleton (usually turned
deep red by a peculiar colouring matter) cleared of the soft animal
investment, as the heart-wood of a tree might be stripped of its bark,
which is the red coral.

In the case of the red coral, the hard skeleton belongs to the
interior of the stem and branches only; but in the commoner white
corals, each polype has a complete skeleton of its own. These
polypes ate sometimes solitary, in which case the whole skeleton is
represented by a single cup, with partitions radiating from its centre
to its circumference. When the polypes formed by budding or division
remain associated, the polypidom is sometimes made up of nothing but
an aggregation of these cups, while at other times the cups are at
once separated and held together, by an intermediate substance, which
represents the branches of the red coral. The red coral polype
again is a comparatively rare animal, inhabiting a limited area, the
skeleton of which has but a very insignificant mass; while the white