There is a very singular group of animals, the HolothuriadÆ, that claims a passing notice, from their near relation in structural formation to the Sea-Urchins, although externally they also exhibit a certain resemblance to the Annelides. They are commonly termed Sea-Cucumbers, from the fancied likeness which they bear, both in shape and colour, to their namesakes of the vegetable kingdom.

A Holothuria is very unattractive in appearance when lying listless upon the sea-beach, but if a small specimen be transferred to the aquarium, it exhibits features of a very singular and interesting character. When about to change its position, the head, hitherto concealed, is protruded and expanded, until it assumes the form of a beautiful flower.

The animal moves principally by aid of sucker-like feet, similar in form to those of the AsteriadÆ, or Sea-Urchins. In most species, the body is divided longitudinally into five rows of suckers. In some, however, these organs are scattered over the entire surface, while in the small Sea-Cucumber (Psolus phantapus), they are arranged in three rows upon a soft, oblong, flat disc, situated beneath the body of the animal, like the foot of a gasteropod mollusc.

Of one genus—the Trepang—many species are eaten by the omnivorous inhabitants of the Celestial Empire, by whom it is employed in the preparation of 'nutritious soups, in common with an esculent sea-weed, shark's fins, edible birds' nests, and other materials affording much jelly.' The intestines, which are generally found to be filled with coral, and solid masses of madreporic rock, are extracted, and the animal then boiled in sea-water and dried in smoke.

Nothing can possibly be less enticing than the black and shrivelled carcases of these defunct gasteropods, as they are seen spread out and exposed for sale in the China markets. There are many varieties of Trepang, some being held in higher esteem than others,—hence the great difference which exists in the price of the article. The lowest quality being ten dollars, and the highest fifty dollars, per pecul of 133 lbs.

The following are titles by which a few of the HolothuriÆ are known in China:—

The illustration on Plate 11 gives a good idea of the typical form of the HolothuriadÆ. It represents a species of the genus Cucumaria, C. communis, or common Sea-Cucumber. Its length is from four to eight inches; but, like all its kindred, it possesses the power of considerably extending or contracting its body at will. The Tentacula are ten in number, pinnate and plumose, stalked and rather large. The body is five-sided, with numerous suckers on the angles, but more on the sides, which are papilose. The colour is yellow, or brownish-white, although specimens found on the Irish coast exhibit a purplish hue.

This, the most common species of its genus, is an inhabitant of deep water, and is therefore most frequently taken with the dredge. Occasionally, specimens may be found after violent storms stranded on various parts of the shores of the United Kingdom.

The Sea-Cucumbers possess the singular power of disembowelling themselves upon the slightest provocation, and also of throwing off their Tentacula entire. There is one species, indeed, that exhibits a still more wonderful phenomenon. At certain times members of this species will divide their body into a number of parts, each of which will in due course become a new and completely-formed animal. After this the reader will be prepared to learn, that to build up a new inside, or create a new set of branchiÆ, is to a Holothuria a very trifling and insignificant task.