The ignorant, like you and I, call the Holothuria the Cornechou, or Sea-cucumber, and perhaps, for two reasons, they are not far wrong. The term sea-cucumber expresses with wonderful exactness the shape of the animal, and its habitation, the sea; and, again, it would puzzle the most learned to explain the word _Holothuria_. The body of this strange creature presents the form of an elongated and worm-like cylinder; its dimensions are so variable that, while some species are only an inch or two in length, others attain thirty and even forty. In general, the skin of the Holothuria is thick and leathery; it includes muscles, and is armed occasionally with small projecting hooks or fangs, which enable the creature to hang for a few seconds on to foreign bodies. From this coriaceous envelope issue tentacular feet analogous to those described in the sea-urchin and sea-star. When we open a Holothuria we find nearly the whole internal cavity occupied with little white tubes. We know that the fabulous cucumber spoken of in the "Arabian Nights" was stuffed with pearls by the talking-bird. With our poor animal this, alas! is not so. These are no pearls, but simple prosaical tubes containing the ova. The mouth opens at the extremity of the body; it forms a sort of funnel, and is surrounded, as by a glory, with an elegant circle of tentacula. In the living animal, when it feels itself in security, these tentacles expand themselves like the corolla of a flower. When the fisherman seizes a Holothuria in the water this crown of tentacles ceases to appear, for the animal has the power of withdrawing it quite suddenly, and now it resembles nothing so much as a common leech. If, however, it is preserved in fresh sea-water and left in peace--if we treat it, in short, with the regard due to its elegant crown of tentacula--this elegant ornament will be expanded in all its glory. Immediately below the mouth is a muscular pharynx, which is contained in a long intestine, with many convolutions, which terminate in the posterior part of the body in an orifice whence is thrown from time to time a little jet of water. The terminal portion of the intestinal canal in these animals is enlarged, introducing us to a system of numerous tubes which branch off into the visceral cavity, receiving the water from without while breathing by its posterior extremity; the animal can at will fill this reservoir or eject the water, and it is by these alternate movements of aspiration and its reverse that it renews the oxygen necessary for respiration. The circulation appears to form a complete circle, there being no heart or central agent; but a ring round the gullet, from which issue five principal nervous chords, represents the nervous system.