nded upon
the living Corals of the outer Reef to-day. There would be among the
Astraeans the different species of Astraea proper, forming the close
round heads,--the Mussa, growing in smaller stocks, where the mouths
coalesce and run into each other as in the Brain-Corals, but in
which the depressions formed by the mouths are deeper,--and the
Caryophyllians, in which the single individuals stand out more
distinctly from the stock; among Porites, the P. Astroides, with pits
resembling those of the Astraeans in form, though smaller in size,
and growing also in solid heads, though these masses are covered with
club-shaped protrusions, instead of presenting a smooth, even surface
like the Astraeans,--and the P. Clavaria, in which the stocks are
divided in short, stumpy branches, with club-shaped ends, instead of
growing in close, compact heads; among the Maeandrinas we should have
the round heads we know as Brain-Corals, with their wavy lines over the
surface, and the Manacina, differing again from the preceding by certain
details of structure; among the Madrepores we should have the Madrepora
prolifera, with its small, short branches, broken up by very frequent
ramifications, the M. cervicornis, with longer and stouter branches and
less frequent ramifications, and the cup-like M. palmata, resembling
an open sponge in form. Every Species, in short, that lives upon the
present Reef is found in the more ancient ones. They all belong to our
own geological period, and we cannot, upon the evidence before us,
estimate its duration at less than seventy thousand years, during which
time we have no evidence of any change in Species, but on the contrary
the strongest proof of the absolute permanence of those Species whose
past history we have been able to trace.

Before leaving the subject of the Coral Reefs, I would add a few words
on the succession of the different kinds of Polyp Corals on a Reef as
compared with their structural rank and also with their succession in
time, because we have here another of those correspondences of thought,
those intellectual links in Creation, which give such coherence and
consistency to the whole, and make it intelligible to man.

The lowest in structure among the Polyps are not Corals, but the single,
soft-bodied Actiniae. They have no solid parts, and are independent in
their mode of existence, never forming communities, like the higher
members of the class. It might at first seem strange that i