existing cognate genera of Cephalopods; we
cannot but infer that these extinct families filled
a larger space, and performed more important
functions among the inhabitants of the ancient
seas, than are assigned to their few living representatives
in our modern oceans.
Conclusion.
It results from the view we have taken of the
zoological affinities between living and extinct
species of chambered shells, that they are all
connected by one plan of organization ; each
forming a link in the common chain, which
unites existing species with those that prevailed
among the earliest conditions of life upon our
globe ; and all attesting the Identity of the design,
that has effected so many similar ends through
such a variety of instruments, the principle of
whose construction is, in every species, fundamentally
the same.
Throughout the various living and extinct
genera of Chambered shells, the use of the air
chambers and siphon, to adjust the specific
gravity of the animals in rising and sinking,
appears to have been identical. The addition
of a new transverse plate within the conical
shell added a new air chamber, larger than the
preceding one, to counterbalance the increase of
weight that attended the growth of the shell and
body of all these animals.
These beautiful arrangements are, and ever
have been, subservient to a common object, viz.
the construction of hydraulic instruments of essential
importance in the economy of creatures
destined to move sometimes at the bottom, and
at other times upon or near the surface of the
sea. The delicate adjustments whereby the same
principle is extended through so many grades
and modifications of a single type, show the
uniform and constant agency of some controlling
Intelligence ; and in searching for the origin
of so much method and regularity amidst variety,
the mind can only rest, when it has passed back,
through the subordinate series of Second causes,
to that great First Cause, which is found in the
will and power of a common Creator.
SECTION VIII.
FORAMINATED POLYTHALAMOUS SHELLS.
Nummulites.
I f the present were a fit occasion for such minute
inquiries, the investigations of the various known
species of Microscopic shells would unfold a
series of contrivances having relation to the economy
of the minute Cephalopods by which they
were constructed, not less striking than those we
have been examining in the shells of extinct