the Sea-Anemone remain always soft, become perfectly solid in the Polyp
Coral and form a frame as hard as bone. It may naturally be asked
where the lime comes from in the sea which the Corals absorb in such
quantities. As far as the living Corals are concerned the answer is
easy, for an immense deal of lime is brought down to the ocean by
rivers that wear away the lime deposits through which they pass. The
Mississippi, whose course lies through extensive lime regions, brings
down yearly lime enough to supply all the animals living in the Gulf of
Mexico. But behind this lies a question not so easily settled, as to
the origin of the extensive deposits of limestone found at the very
beginning of life upon earth. This problem brings us to the threshold of
astronomy, for limestone is metallic in character, susceptible therefore
of fusion, and may have formed a part of the materials of our earth,
even in an incandescent state, when the worlds were forming. But though
this investigation as to the origin of lime does not belong either to
the naturalist or the geologist, its suggestion reminds us that the
time has come when all the sciences and their results are so intimately
connected that no one can be carried on independently of the others.
Since the study of the rocks has revealed a crowded life whose records
are hoarded within them, the work of the geologist and the naturalist
has become one and the same, and at that border-land where the first
crust of the earth condensed out of the igneous mass of materials which
formed its earliest condition their investigation mingles with that of
the astronomer, and we cannot trace the limestone in a little Coral
without going back to the creation of our solar system, when the worlds
that compose it were thrown off from a central mass in a gaseous
condition.

When the Coral has become in this way permeated with lime, all parts of
the body are rigid, with the exception of the upper margin, the stomach,