In the sepia, the teuthis, and the teuthus the hard parts are
within, towards the back of the body; those parts are called in one
the sepium, and in the other the 'sword'. They differ from one
another, for the sepium in the cuttle-fish and teuthus is hard and
flat, being a substance intermediate between bone and fishbone, with
(in part) a crumbling, spongy texture, but in the teuthis the part
is thin and somewhat gristly. These parts differ from one another in
shape, as do also the bodies of the animals. The octopus has nothing
hard of this kind in its interior, but it has a gristly substance
round the head, which, if the animal grows old, becomes hard.