AN EXTEMPORE AQUARIUM.

269

plished this, we left our new vivarium to the surge, which now came rolling in.

The plan succeeded well. Revisiting our tank when the retreating tide had ebbed sufficiently, we found the cover undisturbed, and, on removing it, the water clear and pure, fit to receive whatever specimens the coast afforded. These were soon obtained, and many a happy hour we passed upon that rocky seat, contemplating the various beauteous forms whose history we now must hasten to describe.

CHAPTER XXVII.

PONTOBDELLA MURICATA-SKATE-LEECH.

"Gem, flower and fish, the bird, the brute,
Of every kind occult or known
(Each exquisitely form'd to suit
Its humble lot, and that alone),
Through ocean, earth and air fulfil
Unconsciously their Maker's will."

THE Pontobdella, or Skate-leech (Pl. V. fig. 3), preys on the living skate, and it is said also on other flatfish, sucking their blood, which seems to constitute its proper food. The firm adhesion of the sucker to the skin of its prey must render this animal a cruel and inveterate enemy.

During the day this singular leech reposes in absolute quiescence, but towards evening its wonted coil relaxes into wider curves, and it rears itself erect, with the head turned inwards.

The Skate-leech propagates by eggs or capsules of a very remarkable configuration, which are more or less numerous, according to the fertility of individuals; and they appear either singly, which is rare, or in a considerable group, perhaps fifty, deposited on the exterior or interior surface of a shell.

Each of these capsules consists of a short stalk or

EGGS OF THE SKATE-LEECH.

271

pedicle, surmounted by a spheroid, and supported by a kind of sole or sucker (Pl. V. fig. 3, a, b). The capsule is altogether about three lines in length, and the spheroid, which contains the embryo or young leech, about two lines in diameter. Such capsules are firmly agglutinated by the sole to the substance whereon they are deposited. They are originally white, or of the faintest carnation, of a fine, soft downy aspect, with the neck (stalk) orange or yellowish. They darken gradually from the time of their production, and in four or five days the original white is converted to olive-green or dull wax-yellow. They are produced singly, free from all gelatinous matter.

This capsule is a very singular object, quite peculiar, insomuch that it bears no resemblance to the egg of any other animal. It consists of a coriaceous, tough, thick integument full of tenacious, albumenous, brownish matter. It contains, when mature, only a single embryo, which penetrates the lateral umbo in issuing forth to the light. At this period the young leech is about an inch in length.

The propagation of this species is not strictly confined to any season, though belonging chiefly to the

summer.

The Skate-leech is most patient of abstinence. It is extremely voracious in the natural state, but rejects all subsistence when in confinement, although in such a condition it survives a long time.

CHAPTER XXVIII.

SERPULA AND SPIRORBIS.

"And far beneath the tempest's path
In coral grots defies the foe,
That never brake in heaviest wrath

The sabbath of the deep below."
J. MONTGOMERY.

NATURALISTS divide the Annelida into erratic and sedentary. The former, as may be easily concluded, have no permanent abode; the latter occupy a fixed habitation, sometimes of very durable materials and solid construction. They are themselves its constructors, and many of them real architects of a very ingenious kind.

Among the tube-inhabiting or sedentary Annelides we shall describe a few of those most frequently met with upon our own shores, in order to illustrate their habits and general economy, selecting more especially such species as are best adapted to become residents in the aquarium, either on account of the elegance of their forms, or the interest attaching to their habits.

Every one must have observed that stones, dead shells, fragments of pottery, or any similar substances that have been sunk for a length of time in the sea, become covered over with irregularly-twisted cal

TUBES AND HABITS OF SERPULE.

273

careous tubes, which sometimes accumulate in great abundance; and not unfrequently masses of similar tubes are brought up from considerable depths by the lines of the fisherman. If, while the contained animals are alive, these be placed in a vessel of seawater, few spectacles can be more pleasing than that which they will speedily exhibit. The mouth of the tube is first seen to open by the raising of an exquisitely-constructed door, and then the creature cautiously protrudes the upper part of its body, spreading out at the same time two gorgeous fan-like expansions, of a rich scarlet or purple colour, which float elegantly in the surrounding water, and serve as branchial or breathing organs (Pl. V. fig. 4).

The tube wherein the Serpula (such is the name of these beautiful worms) dwells is calcareous, being formed by an exudation from the creature's body, which, even under water, soon hardens into shell in a manner very similar to that whereby other shells are constructed; and in this tenement the limbless Annelide is of course destined to remain during its whole lifetime, fishing for such food as may be obtainable in the immediate vicinity of its residence.

The habits of these elegant Annelides are necessarily extremely simple. Immoveably fixed by means of their tubes to foreign bodies, and frequently at a considerable depth in the sea, all their movements are restricted to the mere act of protruding the anterior portion of their bodies to a little distance out of their shelly residence, so as to expose their beautiful branchia to the influence of the surrounding element; these, spread out like fans in the water, are