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."

I am sure you will pardon my interrupting your microscopic gazings for a moment by quoting the following charming lines bv the Rev. Dr. Drummond, which were elicited by his having watched with pleasure the elegant form and motions of this little creature :—

" Now o'er the stern the fine-meshed net-bag fling, And from the deep the little Beroe bring : Beneath the sun-lit wave she swims concealed By her own brightness ;—only now revealed To sage's eye, that gazes with delight On things invisible to vulgar sight. When first extracted from her native brino, Behold a small round mass of gelatine, Or frozen dew-drop, void of life or limb : But round the crystal goblet let her swim 'Midst her own element—and lo ! a sphere Banded from pole to pole— a diamond clear, Shaped as bard's fancy shapes the small balloon To bear some sylph or fay beyoud the moon. From all her bands see lucid fringes play, That glance and sparkle in the solar ray With iridescent hues. Now round and round

She wheels and twirls—now mounts—then sinks profound- Now see her, like the belted star of Jove,

Spin on her axis smooth—as if she strove To win applause—a thing of conscious sense, Quivering and thrilling with delight intense. Long silvery cords she treasures in her sides, By which, uncoiled at times, she moors and rides ; From these, as hook-hairs on a fisher's line, See feathery fibrils hang, in graceful twiue, Gracef ul as tendrils of the mantling vine ; These, swift as angler by the fishy lake Projects his fly, the keen-eyed trout to take, She shoots with rapid jerk to seize her food, The small green creatures of crustaceous brood : Soon doomed herself a ruthless foe to find, When in th' Actinia's arms she lies entwin'd. Here prison'd by the vase's crystal bound, Impassable as Styx's nine-fold round, Quick she projects, as quick retracts again, Her flexile toils, and tries her arts in vain ; Till languid grown, her fine machinery worn By rapid friction, and her fringes torn, Her full round orb wanes lank, and swift decay Pervades her frame till all dissolves away. So wanes the dew, conglobed on rose's bud ; So melts the ice-drop in the tepid flood : Thus, too, shall many a shining orb on high That studs the broad pavilion of the sky, Suns and their systems, fade, dissolve, and die."

While we have been admiring our lovely little Cydippe, and comparing notes with other observers and admirers ;. other species as small, as transparent, as sprightly, and scarcely less elegant, have been impatiently waiting for their share of admiration ; shooting to and fro, tossing about their little bells of ductile glass, and alternately lengthening and snatching-in their sensitive tentacles, in astonishment at our stoical indifference to their charms, and saying, after their manner, with the little urchin whose feelings were hurt by the neglect of his papa's visitor,—" You don't notice how beautiful I be !"

A thousand pardons, sweet little Sarsia! We will now give you our undivided attention ; and for this end we must take the liberty of catching you, and of transferring your translucency to solitary grandeur in this other glass.

! but you don't want to be caught, eh 1 And so you pump and shoot round and round the jar as the spoon approaches ! Truly you are a supple little subject, difficult to catch as a flea, and difficult to hold (in a spoon) as an eel. But here you are at last, lying as motionless and as helpless in the silver as a half-melted atom of calf's-foot jelly, to which, indeed, you possess no small resemblance.

Look at the pretty little Medusa in his new abode, at once recovering all his jelly-hood as he feels the water laving him, and dashing about his new domain with a vigour which makes up for lost time.

It is a tall bell of glass a little contracted at the mouth —its outline forming an ellipse, from which about a third has been cut off. The margin of this bell carries four tiny knobs, set at equal distances, and thus quartering the periphery ; and these are the more conspicuous, because each one is marked with a bright orange-coloured speck. Physiologists are pretty well agreed to consider such specks as these, on the margins of the smaller Medusce, as eyes,—rudimentary organs of vision, capable, probably, of appreciating the presence and the stimulus of light, without the power of forming any visual image of external objects. You will not gain much information about their function from microscopic examination ; for all you can discern is an aggregation of coloured specks (pigment-granules) in the midst of the common jelly.

The knobs, however, are connected with other organs ; for from each of them depends a highly sensitive and very contractile tentacle. Sometimes one, or more, or all, of these organs hang down in the water motionless, lengthening more and more, especially when the bell is still, until they reach a length some twelve or fifteen times that of the bell, or umbrella. Then suddenly one will be contracted, and, as it were, shrivelled, to a mere fragment a quarter of an inch long ; then lengthened again to an inch or two; then shortened again. Now the little bell resumes its energetic pumping, and shoots round and round in an oblique direction, the summit always going foremost, and the tentacles streaming behind in long trailins lines. Now it is acrain arrested : the bell turns over on one side and remains motionless, and the tentacles, "fine as silkworm's threads," float loosely in the water, become mutually intertangled, instantly free themselves pucker and shrivel up, slowly lengthen, and hang motionless again, or, as the bell allows itself to sink slowly, are thrown into the most elegant curves and arches.

Though these tentacles look at first like simple threads of extreme tenuity, yet when viewed closely they are seen to be composed of a succession of minute knobs separated by intervals, like white beads strung on a thread ; the beads being more remote from each other in proportion as the tentacle is lengthened.

This structure is worthy of a more minute investigation. We will therefore confine our little Sarsia in this narrow glass trough, which is sufficiently deep to allow its whole form to be immersed, though somewhat flattened; which is an advantage, as its movements are thereby impeded. Now, with a power of 300 diameters, you see that each of the knobs of the tentacle is a thickening or swelling of the common gelatinous flesh, in which are imbedded a score or two of tiny oval vesicles, or bladders, without any very obvious arrangement; but for the most part so placed that the more pointed end of each is directed towards the circumference of the thickening. The intermediate slender portions of the tentacle—the thread on which the beads are strung— is quite destitute of these vesicles.

These little bodies are called cnidce; and, in the whole of this class of animals, and also in that of Zoophytes, they play an important part in the economy of the creature. I shall probably take occasion to exhibit them to you under conditions more favourable than are presented here, viz., in the Sea-Anemones, where they attain far greater dimensions; and therefore I will merely say here that each one of these tiny vesicles carries a barbed and poisoned arrow, which can be shot forth at the pleasure of the animal with great force, and to an amazing length; that hundreds are usually shot together; and that this is the provision which the All-wise God has given to these apparently helpless animals for securing and subduing their prey. There is, however, another organ still more conspicuous in our little Sarsia, of which I have not yet spoken. As the whole animal has the most absolute transparency, we see that the roof of the bell is much thicker than the sides, and that it graclually thins off to the edge. The interior surface is called the subumbrella, and it carries within its substance four slender tubes, which, radiating from the centre of the roof, proceed to the margin, where they communicate with another similar canal which runs round the circumference, sending off branches into the tentacles. This is the circulatory system; and you may see, with the magnifying power which you are at present using, that a clear fluid is moving rapidly within all these canals, carrying minute granules; not with an even forward current, but with an irregular jerking movement, as if several conflicting eddies were in the stream. Yet we discern that, on the whole, the granules are moved forward; passing from the centre of

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