at like its protection better than
exposure to the open sea, just as many land-animals prefer the close and
shaded woods to the open plain: a forest is not more thickly peopled
with Birds, Squirrels, Martens, and the like, than is the Coral Reef
with a variety of animals that do not contribute in any way to its
growth, but find shelter in its crevices or in its near neighborhood.

But these larger animals are not the only ones that haunt the forest.
There is a host of parasites besides, principally Insects and their
larvae, which bore their way into the very heart of the tree, making
their home in the bark and pith, and not the less numerous because
hidden from sight. These also have their counterparts in the Reef, where
numbers of boring Shells and marine Worms work their way into the solid
substance of the wall, piercing it, with holes in every direction, till
large portions become insecure, and the next storm suffices to break off
the fragments so loosened. Once detached, they are tossed about in the
water, crumbled into Coral sand, crushed, often ground to powder by the
friction of the rocks and the constant action of the sea.

After a time, an immense quantity of such materials is formed about a
Coral Reef; tides and storms constantly throw them up on its surface,
and at last a soil collects on the top of the Reef, wherever it has
reached the surface of the water, formed chiefly of its own _debris_, of
Coral sand, Coral fragments, even large masses of Coral rock, mingled
with the remains of the animals that have had their home about the
Reef, with sea-weeds, with mud from the neighboring land, and with the
thousand loose substances always floating about in the vicinity of a
coast and thrown upon the rocks or shore with every wave that breaks
against them. Add to this the presence of a lime-cement in the water,
resulting from the decomposition of some of these materials, and we have
all that is needed to make a very compact deposit and fertile soil, on
which a vegetation may spring up, whenever seeds floating from the
shore or dropped by birds in their flight take root on the newly formed
island.

There is one plant belonging to tropical or sub-tropical climates
that is peculiarly adapted by its mode of growth to the soil of these
islands, and contributes greatly to their increase. This is the
Mangrove-tree. Its seeds germinate in the calyx of the flower, and,
before they drop, grow to be little brown stems, some