The disk is meanwhile enlarging its area ; and the spines and suckers, gradually lengthening, at length push themselves through the walls of the helmet; the hanging points and crest of which are fast diminishing by a kind of insensible absorption ; the ciliary movements become less vigorous,and the mouth closes up. But, correspondently, the Urchin isbeginning to acquire its own independent power of locomotion; for the suckers, now ever sprawling about, are capable of adhering to any YOU>*G SEA-VRCHIN: which DEVELOPMENT OF DISK. foreign body with they come into contact, and of dragging the whole structure about, by their proper contractions. The cilia that cover the thickened fringing band still exercise their powers, and are the last to disappear. x

When the disk has grown to such an extent as to spread over about half of the larval stomach, very little remains of the helmet, except the middle portions of the glassy rods and the ciliary bands; all the rest of this exquisitely modelled framework having vanished by insensible degrees, no one knows how or where. The stomach and gullet, indeed, are gradually sucked into the ever-growing disk ! But all the rest, flesh and rods, fringes, bands, and cilia, waste away to nothing.

The mouth of the larva has no connexion with the mouth of the Urchin. The little isolated patches of glassy network continue to spread through the flesh of the disk, until the whole forms one uniform structure, and constitutes a series of plates. The mouth is that spot in the centre, over which the calcareous frame is last extended ; and it is first distinguishable by the appearance of five glassy points, which soon develop themselves into the five converging jaws, which we see forming such a curious apparatus on the inferior side of the Sea-Urchin.

Actual observation has not traced the infant animal beyond this stage of the development ; but Professor Miiller has taken specimens, swimming in the sea, in which scarcely a rudiment of the larva remained. They had the form of round flattened disks, which freely moved their spines, and crawled about the sides of the vessel in which they were kept by means of their suckers, exactly in the manner of the adult Urchin.

"Thus ends this strange, eventful history;" and in reviewing it, one can scarcely avoid being impressed with a sense of the majesty of God in these His humbler works. By what wonderful, what unexpected roads does He arrive at the completion of His designs ! And if such things as these are only now bursting upon our knowledge, after thousands of years of man's familiar contact with the inferior creatures, how many more wonders may yet remain to be unfolded, as science pursues her investigations into the Divine handiwork !

Chapter XVII. Jelly-fishes

As this afternoon was delightfully calm and warm, the very model of an autumnal day, I took my muslin ringnet and walked down to the rocks at the margin of the quiet sea. Nor was I disappointed ; for the still water, scarcely disturbed by an undulation, and clear as crystal, was alive with those brilliant little globes of animated jelly, the Ciliograde and Naked-eyed Medusae, apparently little more substantial than the clear water itself. Multitudes of them were floating on the surface, and others were discerned by the practised eye, at various depths, shooting hither and thither, now ascending, now descending, now hanging lightly on their oars, and now, as if to make up for sloth, darting along obliquely with quicklyrepeated vigorous strokes, or rolling and revolving along, in the very wantonness of humble happiness.

After gazing awhile with admiration at the undisturbed jollity of the hosts, I made a dip with my net, the interior of which, on lifting it from the water, was lined with sparkling balls of translucent jelly. They were far too numerous to allow me to transfer them all to captivity ; they would soon have choked up and destroyed one another ; I therefore selected the finest and most interesting, shaking an example or two of each kind into my glass jar of sea-water, where they immediately began to frolic and revel as if still in the enjoyment of unrestricted liberty. And here they are.

Among these bright and agile beings which are shooting x 2 their wayward traverses across each other, and intertwining their long thread-like tentacles, we will select one or two for examination, as samples of their kindred. And first let me separate this active little Beroe (Cydipjjepomiformis), which I dip out with a tea-spoon and transfer to this other glass jar, that we may watch its form and movements unaffected by the presence of its companions.

We see, then, a little ball, almost perfectly globular, except that a tiny wart marks one pole, of the size of a small marble, and apparently turned out of pure glass, or ice, or jelly—according to your fancy,—perfect transparency and colourlessness being its characteristics ; so much that it is not always easy to catch sight of the little creature, except when we allow the light to fall on the jar in a particular direction. From two opposite sides of the globe proceed two threads of great length and extreme tenuity, which display the most lively and varied movements.

These filaments shall occupy us for a few moments. We trace them to their origin, and find that they proceed each from the interior of a lengthened chamber, on each of two opposite sides of the animal. Suddenly, on the slightest touch of some foreign object, one of the threads is contracted to a point and concealed within its chamber, but is presently darted forth again. When the lovely globe chooses to remain still, the threads hang downward, gradually lengthening more and more, till their extremities lie along the bottom of the jar extended to a length of six inches from the chamber. Then we see that this delicate thread is not simple, but is furnished along one side, throughout its length, at regular distances, with a row of secondary filaments, which project at right angles from the main thread.

These secondary filaments constitute an important element in the charm which invests this brilliant little creature. They are about fifty in number on each thread, and some of them are half an inch long, when fully extended, but it is seldom that we see them thus straightened; for they are ever assuming the most elegant spiral coils, which open and close, extend and contract, with an ever changing vivacity. The animal has a very perfect control over each thread, as well as over each individual secondary filament. They are, either together or separately, frequently projected from their chambers to their full extent, by one impulse; sometimes the extension is arrested at any stage, and then proceeded with, or the thread is par tially or entirely retracted. Sometimes the secondary filaments are coiled up into minute balls, scarcely perceptible, or only so as to give to the thread the appearance of small beads remotely strung on a fine hair; then a few uncoil and spread divergently ; contract again, and again unfold; or many, or all, interchange these actions together, with beautiful regularity and uniformity, repeating the alternation for many times in rapid succession.

The beauty and diversity of the forms assumed by these elegant organs beguile us to watch them with unwearied interest, and we wonder what is their function. For, with all our watching, this is by no means clear. They are certainly not organs of motion. At times it seems as if they were cables intended to moor the animal, while it floats at a given depth; for we see them with their extremities spread upon the bottom, to which they appear to have a power of adhering, thus forming fixed points, from which the little globe rises and falls at pleasure, shortening or lengthening its delicate and novel cables, maintaining all the while its erect position.

When the Cydippe swims, however, which it does with great energy, the threads seem unemployed, streaming loosely behind, and evidently taking no part in the progression, though still adding beauty and grace to the tout ensemble. The organs by which the sprightly motions of the whole animal are effected are of quite another character, and shall now engage our attention.

. You have doubtless observed, while gazing on the animal, a peculiar glittering appearance along its sides, mingled in certain lights with brilliant rainbow-reflections. Now let us take an opportunity, when it approaches the side of the glass, to examine this appearance with a lens. The globe, you see, is marked by longitudinal bands, eight in number, set at equal distances, and ranging like meridians, except that they do not quite reach to either pole. These bands are the seats of the motile organs, which are highly curious, and in some sort peculiar.

Each band is of considerable width in the middle, but becomes narrower towards the extremities. It carries a

number—usually from twenty to thirty—of flat thin membranous fins, set at regular distances, one above the other, which may be considered as single horizontal rows of cilia, agglutinated together into flat plates. Each plate has a rapid movement up and down, from the line of its insertion into the band, as from a hinge, and thus striking the water downwards, like a paddle. The whole band may be likened to the paddle-wheel of a steamer, except that the paddles are set in a fixed line of curvature

instead of a revolving circle. The effect, however, is exactly the same : that of paddling the beautiful little globe vigorously through the water. The prismatic colours are produced by the play of light on their glittering surfaces, which are ever presented to the eye of the beholder at changing angles.

We rarely see these rows of paddle-fins wholly at rest, but occasionally one or two bands will be alone in a state of vibration ; or one or more will suspend their action while the rest are paddling. Sometimes, in a band that is at rest, a minute and momentary wave will be seen to run rapidly along its length. All these circumstances show that the ciliary motion is perfectly under the control of the animal's will, not only in the aggregate, but in every part.

In an excellent memoir on this animal by Mr. It. Patterson, of Belfast,* there are some interesting observations on the power of its tissues to become tinged with extraneous colours, a fact which may be useful to you in your researches, as enabling you with more ease and precision to demonstrate the internal structure.

" From the inconsiderable quantity of solid material (remarks this observer) " which enters into the body of the Beroes, and the rapid circulation of water, which is apparent throughout their frame, we would naturally suppose that any tinge which the body might accidentally acquire would be extremely fugitive. It was found, however, to be much less so than a priori would have been expected. My attention was drawn to this peculiarity by the circumstance of all my glass vessels being one evening occupied by Beroes and Crustacea, so as to compel me to place a small Medusa in a tin vessel, which chanced to be rusted at the seams. Next morning the colourless appearance of the animal was changed into a bright yellow, which appeared to pervade every part, and doubt- * "Trans. Roy. Irish Academy," vol. xix. pt. 1.

less arose from the oxide of iron, diffused through the sea-water. This tint remained during the entire day, although the animal was transferred to pure sea-water. Wishing to try if the vessels of the Beroe would become distinct, if filled with some coloured fluid from which the animal could suddenly be withdrawn, and viewed through the usual transparent medium of sea-water, I placed a Beroe in a weak infusion of saffron. At the end of twenty minutes its colour had undergone a perceptible change. I allowed it, however, to remain immersed for about six or seven hours, when it had assumed a bright yellow hue. It was then placed in pure sea-water, but retained its yellow colour for twenty-four hours afterwards; and though it gradually became fainter, it was very perceptible even at the expiration of forty-eight hours."

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