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The beaks of Cuttle-fishes, though not abundant, are sufficiently
plentiful to have earned for themselves the general title of
"Rhyncholites;" and in their form and function they resemble
the horny, parrot-like beak of the existing Cephalopods. The
ink-bag or leathery sac in which the Cuttle-fishes store up the
black pigment with which they obscure the water when attacked,
owes its preservation to the fact that the colouring-matter which
it contains is finely-divided carbon, and therefore nearly
indestructible except by heat. Many of these ink-bags have been
found in the Lias; and the colouring-matter is sometimes so well
preserved that it has been, as an experiment, employed in painting
as a fossil "sepia." The "pens" of the Cuttle-fishes are not
commonly preserved, owing to their horny consistence, but they
are not unknown. The form here figured (_Beloteuthis subcostata_,
fig. 172) belonged to an old type essentially similar to our modern
Calamaries, the skeleton of which consists of a horny shaft and
two lateral wings, somewhat like a feather in general shape. When,
on the other hand, the internal skeleton is calcareous, then it is
very easily preserved in a fossil condition; and the abundance of
remains of this nature in the Secondary rocks, combined with their
apparent total absence in Palaeozoic strata, is a strong presumption
in favour of the view that the order of the Cuttle-fishes did
not come into existence till the commencement of the Mesozoic
period.
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