Thus we see one use of the hooked tip is to afford a stronger spring;
but it has a more direct bearing on the burrowing habits of the animal.
Like all the rest of its beautiful tribe, this species is a dweller in
the deep sand, into which it can penetrate with considerable power and
rapidity. In order to do this, the foot is straightened, and the sharp
point is thrust perpendicularly down into the wet sand. The muscular
force exerted is sufficient to penetrate the soft sand to the whole
length, when the point is suddenly bent sidewise, thus obtaining a
strong holdfast. The whole organ is now strongly contracted in length,
and the animal and shell are dragged forcibly to the mouth of the
burrow, the edges of the valves downward and piercing the sand a little
way. The straightened point is then pushed an inch or two farther
down; again hooked, and another pull is made. The shell descends a
little farther into the yielding sand, and the same interchange of
processes goes on till the animal is sufficiently buried. To read
this description you would suppose it a most clumsy, and ineffective,
and slow business; but indeed this is very far from its character. The
elongations and contractions are made with great rapidity; and almost
with the quickness of thought the unwieldy cockle, when in full vigour
and thoroughly alarmed, disappears into his sandy fortress; so fast,
indeed, that you must be very alert to overtake him and prevent his
descent, if you have no appliances but your two hands.
Cuvier, in his elaborate and beautiful dissections of the Mollusca,
has demonstrated that this important organ is mainly composed of an
immense multitude of muscles, circular, longitudinal, and transverse,
wonderful in their complexity and arrangement, but most perfectly
adapted to impart variety, force, and precision to its movements. In
these respects the human tongue perhaps presents the closest parallel
to its organization. It is remarkable that at its upper or basal part
it is hollow, and encloses some of the viscera of the body.