prepared a fitting surface for different kinds of Corals that could not
live in the depths from which the Astraeans have come, but find their
genial home nearer the surface; such a home being made ready for them
by their predecessors, they now establish themselves on the top of the
Coral wall and continue its growth for a certain time. These are the
Mandrinas, or the so-called Brain-Corals, and the Porites. The Mandrinas
differ from the Astraeans by their less compact and definite pits. In
the Astraeans the place occupied by the animal in the community is
marked by a little star-shaped spot, in the centre of which all the
partition-walls meet. But in the Mandrinas, although all the partitions
converge toward the central opening, as in the Astraeans, these central
openings elongate, run into each other, and form waving furrows all over
the surface, instead of the small round pits so characteristic of the
Astraeans. The Porites resemble the Astraeans, but the pits are smaller,
with fewer partitions and fewer tentacles, and their whole substance is
more porous.

But these also have their bounds within the sea: they in their turn
reach the limit beyond which they are forbidden by the laws of their
nature to pass, and there they also pause. But the Coral wall continues
its steady progress; for here the lighter kinds set in,--the Madrepores,
the Millepores, and a great variety of Sea-Fans and Corallines, and the
reef is crowned at last with a many-colored shrubbery of low feathery
growth. These are all branching in form, and many of them are simple
calciferous plants, though most of them are true animals, resembling,
however, delicate Algae more than any marine animals; but, on
examination of the latter, one finds them to be covered with myriads of
minute dots, each representing one of the little beings out of which the
whole is built.