P. H. GOSSE, _del._ LEIGHTON, BROS.
DOTTED SIPONCLE. SEA-CUCUMBER.
]
The suckers, which, when the animal first came into our possession,
were apparent only as little warts, arranged in five clustered rows
down the angles of the body, are now seen to be long tubes, each
with an adhering disk at its extremity, by which it anchors to the
surrounding stones. The mechanism of these suckers does not importantly
differ from that of the same organs in the Star-fishes. Indeed,
notwithstanding the very wide diversity of form and appearance between
the two animals, the Cucumber and the Star are so nearly allied as to
belong to the same class, that named ECHINODERMATA; the Sea-urchins,
creatures totally diverse in aspect from both, connecting the forms
together.
And this Cucumber, again, is connected with the proper worms
(ANNELLIDA) by some obscure animals which bear the name of Siponcles.
Here is one which may illustrate the form, the Dotted Siponcle.[14]
It has a cylindrical body, rounded and abruptly pointed behind, which
is of a light-brown hue, with a satiny gloss; but the hue resolves
itself under a powerful lens into a freckling of pale dots, excessively
numerous, on a brown ground, and the lustre into a multitude of
close-set annular wrinkles. What is curious in the creature is the
protrusion and retraction of its trunk. From the front end of the
body we see rapidly protruding, by evolution of the parts, a rather
slender trunk, till it attains about one-third the length of the body;
then its tip expands, and is seen to be surrounded by eight rows of
black points, and within these a circle of slender, white, thread-like
tentacles. These latter are the representatives of the gorgeous
head-plumes of the Cucumber. Immediately the long trunk is turned out
to the outmost, it begins to be rolled in again; and this process goes
on with equal rapidity till it is quite concealed. Then again it is
unrolled, and so on alternately. Doubtless the function of respiration
is performed by this action; and perhaps also food is collected and
swallowed.