moveable tooth, which plays up and down. When the cone is put together, the flat, dressed surfaces of the five jaws, which stand round in a circle, are brought into contact. All the food which is received at the mouth must pass between these surfaces; and as there are systems of muscles which enable them to play up and down and across, a more perfect mill for grinding down the food cannot well be conceived. We have not space more fully to describe it, but the excellent popular account given by Professor Jones,* and the examination of a living specimen, will enable any one to understand the uses of the several parts of this singular mechanism.

Of the same class with the Sea Urchins and Starfishes, but exhibiting its characters in a weaker degree, and showing in form and structure a tendency towards the Annelides, are the Holothuriada, or Sea Cucumbers, of which several species occasionally come up in the dredge. Their name, Sea Cucumbers, is very expressive of their form in a contracted state, when the body shrinks up into an oblong mass, slightly tapering to each end, and rough with wrinkles and with the rows of sucking-feet, which it has in common with the Urchins and Star-fishes. In its texture it is tough and leathery, without calcareous plates. The absence of a shell, the presence of feathery tentacula about the mouth, and the shape of the body, are differences between these creatures and the Urchins ; while the two latter circumstances, together with the mode of progression by alternate contractions and extensions of the body, connect them with the Annelides. The general form of this

"General Outline of the Animal Kingdom," p. 166, &c.

family may be understood from the annexed figure, which represents Thyone papillosa, a species found on various parts of the coast. It differs from other animals of the family chiefly by having its sucking-feet scattered in an irregular manner over the whole surface, instead of being confined to five rows along the angles of the body. In other respects it resembles most of its kindred. Its length is about three inches, but it can at pleasure extend and contract considerably. The colour is a dusky brownish white, sometimes varied with spots. The tentacula, commonly whitish, are ten in number, pinnate, and capable of being much expanded, or wholly retracted within the orifice of the mouth. In captivity it is not always easy to persuade it to put forth these delicate organs to their full extent, but a bath of clean water will often put it into good-humour. We have already noticed the self-destruction of some

184

DEEP-SEA ZOOPHYTES.

of the Star-fishes: the Sea Cucumbers have an equally singular habit of a similar kind. As their skin is too tough and strong to admit of voluntary dismemberment, they resort to the unique mode of vomiting up their intestines-in fact, the whole of their internal organs. Yet it does not appear that life is destroyed by this process. At least, it does not suddenly cease; and, according to the observations of Sir J. G. Dalyell, the lost parts are renewed, after months have elapsed, even in cases where the disemboweling process has been carried to an extreme point, leaving "the body an empty sac." Holothuria are often taken with their internal parts more or less deficient, yet apparently existing in health and vigour : in such, probably, the lost parts are in process of restoration.

Many interesting members of the class of Zoophytes, or compound Polypes, are met with in dredging, a general account of whose classification has been given in a former chapter. For a more specific account of the deep-sea species, I must refer to Dr. Johnston's admirable work on the subject, and will here just notice some of the other ASTEROIDA, which I purposely omitted when speaking of the other two orders, HYDROIDA and HELIANTHOIDA. This group is distinguished from either of the others by a readily seen character, namely, the softer parts of the compound animal invest and enclose the harder parts, or skeleton. The coral of all this group is therefore internal. The precious coral of commerce is the skeleton of one of these Zoöphytes; and so is the Gorgonia flabellum, or Venus's Fan, a well-known West Indian species, which forms a beautiful network, strength

The

ened by a branching system of ribs, like the ribs and fibres of a skeleton leaf. Four British species of Gorgonia, one of them common on the Devonshire coast, are recorded. G. verrucosa, the commonest of these is from six to twelve inches high, and much branched, like a tree; but its branches do not form a network. Its coral has a dense, black axis of a horny substance, which encloses a white pith, and is coated with a whitish crust, covered with warts, arranged in somewhat spiral lines. Such is the aspect of the dried Polypidom. When living, the crust is soft and flesh-coloured. Alcyonium, another member of this order, has already been noticed. More interesting and beautiful forms are found in the family of Pennatulidæ or Sea-pens, of which three species, arranged under as many genera, are natives of Britain. These curious animals present us with the fact of compound bodies, in all respects analogous to corals, existing in an unattached state (that is not rooted or fixed to any base, but freely planted in soft mud), and possibly capable of a motion through the water from place to place. The fact of this motion has been asserted by several naturalists, but observations are wanting in corroboration. The Sea-pen itself (Pennatula phosphorea) is one of the most singular and beautiful of the British Zoöphytes. The Polypidom is three or four inches in length, fleshy, of a purplish red colour, narrow and naked at the lower end, and feathered on its upper half with long, closely-set pinnæ, along the margins of which the polype-cells are placed. These pinnæ are obliquely curved backwards, and capable of separate or united motion; and they have been supposed,

186

VIRGULARIA MIRABILIS.

VIRGULARIA MIRABILIS.

by authors who believe in the swimming powers of this Zoophyte, to have the regular oar-like motion of fins. Through the centre of the stalk runs a calcareous column, which serves to stiffen the body of the Polypidom. When irritated, this Zoophyte is brilliantly phosphorescent; but it does not emit light unless disturbed, or under the influence of pain. Professor Forbes has remarked that, when it is touched, the luminosity commences at the point of contact, and proceeds upwards to the Polypiferous portion of the Zoophyte, but never in a contrary direction; and when the centre of the polypiferous portion is struck, the Polypes below the injury are not affected, while those above it emit light. "When thrown into fresh water, Pennatula scatters sparks about in all directions,-a most beautiful sight." The

the

Virgularia mirabilis is another of this family, closely