Now there is
no mineral body which presents any structure comparable to this,
and the conclusion suggested itself that the Belemnites must be
the effects of causes other than those which are at work in
inorganic nature. On close examination, the saucer-shaped
partitions were proved to be all perforated at one point, and
the perforations being situated exactly in the same line, the
chambers were seen to be traversed by a canal, or
siphuncle, which thus connected the smallest or aphical
chamber with the largest. There is nothing like this in the
vegetable world; but an exactly corresponding structure is met
with in the shells of two kinds of existing animals, the pearly
Nautilus and the
Spirula, and only in them. These
animals belong to the same division--the
Cephalopoda--as
the cuttle-fish, the squid, and the octopus. But they are the
only existing members of the group which possess chambered,
siphunculated shells; and it is utterly impossible to trace any
physiological connection between the very peculiar structural
characters of a cephalopod and the presence of a chambered
shell. In fact, the squid has, instead of any such shell, a
horny "pen," the cuttlefish has the so-called "cuttle-bone," and
the octopus has no shell, or, at most, a mere rudiment of one.
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