flashes are emitted; and should different parts of the sides of the vivarium be occupied by several specimens, as is always the case where miscellaneous collections have been recently introduced, so many brilliant coruscations will escape from all the parts of the vessel where they are established. This interesting, though rude experiment, may be repeated several times upon the same subjects; however, if these are to be preserved, the vessel must be speedily drained and refilled with their proper element, as few marine animals can survive even a short immersion in fresh water.

The Nereis noctiluca is at all times an elegant and instructive little creature, serving at least to show what various forms of life Nature has lighted up to beautify the deep,

"Or gild the surge with insect sparks that swarm

Round the bright oar."

We have yet to discuss one of the most interesting departments connected with the history of the Nereides, namely the metamorphoses which these creatures undergo after leaving the egg, and their subsequent growth to their mature condition,-subjects which, to every aquariist, present a rich field for observation and research.

We need hardly say, that the Nereis, in the earlier stages of its growth, does not as yet possess the almost countless segments that it afterwards acquires; and yet the mode in which those segments become multiplied, and, as they grow, provided with the complicated limbs they sometimes bear, was, until recently, a most unfathomable mystery.

The Nereis, when it leaves the egg, is quite a limb

and might be taken swimming about by How long the micro

less embryo (Pl. VI. fig. 7, a), for an Infusorial form of life, means of a broad ciliated disk. scopic atom keeps this shape we know not, nor the Imode in which it is transformed into the second aspect under which it shows itself (Pl. VI. fig. 7, b), in which condition it is recognizable under a figure somewhat like its proper self, about a line in length, offering as yet only four segments bearing lateral oars, although its head and eyes are quite discernible, as well as one small pair of antennæ.

As growth advances, other segments show themselves successively, and these are always found to be developed in one spot, namely between the last-formed segment and the tail, or rather the tail-bearing ring which terminates the body; and as they by degrees are perfected, they develope from their sides the lateral oars, which now become the locomotive agents, and the creature gradually attains the appearance seen in the next figure (Pl. VI. fig. 7, c).

By constant repetitions of the same procedure, more segments and more oars progressively are added from behind to those in front (Pl. VI. fig. 7, d), until the animal, at length promoted to its perfect form, continues to grow longer as new segments show themselves, till it acquires the complement allowed by Nature in its adult state.

Such is, in brief, an outline of the process; but there yet remains wide scope for any one, whose leisure or whose opportunity affords the means of adding to our knowledge on a subject so important, and as yet almost in its infancy.

CIRRATULUS BOREALIS.

327

CHAPTER XXXIII.

CIRRATULUS BOREALIS "THE NORTHERN CIRRATULUS."

THE length of this beautiful Annelide (Pl. VI. fig. 4) is about four inches; its body is composed of numerous segments tapering towards each extremity; but the most striking feature whereby it is distinguished consists in the possession of numerous long and flexible cirrhi, or thread-like appendages, made up of an infinite number of rings attached along the entire length of its body.

These cirrhi, apparently

"More soft and sensible

Than are the tender horns of cockled snails,"

arise on each side from every alternate segment of the body, and besides being instruments of prehension, apparently perform the functions of the branchiæ or breathing organs of other Annelidans. They run in two rows down the back, and are continued nearly to the posterior extremity; they are longest, however, in the vicinity of the head, becoming gradually shorter as they recede backwards. When the animal crawls, these cirrhi lie along the back, presenting a very singular appearance.

The colour of the Cirratulus is generally red, some

times tolerably vivid; or it is brownish or variegated, owing to the quantity of mud which the worm swallows, apparently as its ordinary diet.

Through its long filamentous arms and branchia the blood ebbs and flows, dyeing them of the richest crimson, or leaving them of a faint yellow colour. The tangled skein which they have formed consists of living coils, ever binding and unbinding their glistening knots, and catching up grains of sand, or atoms of slime, till the animal retires into an envelope of fragments, which, by clustering together, become a case, which encloses and protects it.

The natural and favourite habitat of these Annelides is in the muddy fissures of rocks, or under tufts of sea-weed or other soft covering, and they are generally met with considerably above low-water mark. They are distributed very profusely upon most shores, but are never to be found amongst sand. While the animal lurks in its retreat, its cirrhi are spread like so many worms over the neighbouring surface.

The Cirratulus retires from the light. If kept in a white saucer covered with a shell or stone, it will creep out at night; or by filling the vessel containing it to such a height that the tips of the cirrhi cannot reach the surface of the water, it will abandon its concealment and crawl up the side, thus affording a satisfactory view of its structure; but, when forcibly removed, the whole creature contracts into a confused bunch.

The Cirratulus lays its eggs during the months of May and June: the ova are very numerous, minute.

CONDITION ON LEAVING THE EGG.

329

and of a spherical shape. When hatched, the embryos have exactly the appearance of Infusorial animalcules; in form they are elongated, flattened, and begirt with cilia; their length three times their breadth; their colour a faint dingy yellow; their body generally opaque, but with lighter portions on some specimens. Their movements towards the end of June become rather slow, and sometimes the little creatures display a tendency to revolve horizontally on the centre of the body as on an axis. The further development of these embryos has not as yet been satisfactorily traced.

The Cirratulus is tolerably patient under confinement: one specimen survived eighteen months, and then it perished accidentally.