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But the Cephalopoda and the turbinated Testacea have in common an
arrangement which stands in contrast with this. For here the two
extremities are brought together by a curve, as if one were to bend
the straight line marked E until D came close to Such, then, is the
disposition of the internal parts; and round these, in the
Cephalopoda, is placed the sac (in the Poulps alone called a head),
and, in the Testacea, the turbinate shell which corresponds to the
sac. There is, in fact, only this difference between them, that the
investing substance of the Cephalopoda is soft while the shell of
the Testacea is hard, nature having surrounded their fleshy part
with this hard coating as a protection because of their limited
power of locomotion. In both classes, owing to this arrangement of the
internal organs, the excrement is voided near the mouth; at a point
below this orifice in the Cephalopoda, and in the Turbinata on one
side of it.
Such, then, is the explanation of the position of the feet in the
Cephalopoda, and of the contrast they present to other animals in this
matter. The arrangement, however, in the Sepias and the Calamaries
is not precisely the same as in the Poulps, owing to the former
having no other mode of progression than by swimming, while the latter
not only swim but crawl. For in the former six of the feet are above
the teeth and small, the outer one on either side being the biggest;
while the remaining two, which make up the total weight, are below the
mouth and are the biggest of all, just as the hind limbs in quadrupeds
are stronger than the fore limbs
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