In molluscs the external parts are as follows: in the first place,
the so-called feet; secondly, and attached to these, the head;
thirdly, the mantle-sac, containing the internal parts, and
incorrectly designated by some writers the head; and, fourthly, fins
round about the sac. (See diagram.) In all molluscs the head is found
to be between the feet and the belly. All molluscs are furnished with
eight feet, and in all cases these feet are severally furnished with
a double row of suckers, with the exception of one single species of
poulpe or octopus. The sepia, the small calamary and the large
calamary have an exceptional organ in a pair of long arms or
tentacles, having at their extremities a portion rendered rough by
the presence of two rows of suckers; and with these arms or tentacles
they apprehend their food and draw it into their mouths, and in
stormy weather they cling by them to a rock and sway about in the
rough water like ships lying at anchor. They swim by the aid of the
fins that they have about the sac. In all cases their feet are
furnished with suckers.