antique urns, elevated on the extremities of long and very slender stalks, as slender as threads, and about six times as long as the vases. The stalks grow from the midst of the floccose rubbish attached to the plant, and diverge as they ascend, thus carrying their lovely bells clear of one another.

Each vase is elegantly ventricose, or swollen, in the

middle, terminating below in a kind of nipple to which the stalk is attached, and above in a short wide neck with a thickened rim. This last is highly sensitive and contractile ; its inner edge is set round with a circle of vibratile cilia, which, when in full play, produce a pair of small circular whirlpools over two opposite points of the brim. The cilia themselves cannot be distinguished, but their optical expression is curious. At the two opposite points of the circular margin, as seen in perspective when slightly inclined towards the observer, viz., at those points where the cilia, from their position with regard to the eye, would be crowded together, there are seen two dark dashes, representing, doubtless, two ciliary waves, but which have all the appearance of tangible objects, sometimes withdrawn, sometimes protruded, and often vibrated with a rapid snatching movement.

These vases are of the usual appearance in Infusoria. Their substance is the clear transparent colourless sarcode, but it contains within it more or less of the cloudy nebulous matter which we have been lately familiar with. There are several globular vesicles or vacuoles, some ready to imbibe colour from pigment, and others already occupied with brown food ; while in each case we see, near the centre of the vase, a longish body of clear granular texture, which is called the nucleus, and which seems to play an essential part in the vital economy of the animal.

The movements of a group such as that we are looking at are very sprightly and pleasing. The vases turned in all directions, some presenting their mouths, some their sides, some their bases, to the eye ; inclined at various angles from the perpendicular, and bending in diverse degrees upon the extremity of their stalks; swaying slowly and gracefully to and fro, as driven hither and thither by the ciliary currents; and, above all, ever flying up and down within the length of their radius, as a bird when confined by a string ;— all these circumstances 2 d 2 impart a charm to this elegant animalcule, which enables us to look long at it without weariness.

This last movement is peculiar, and worthy of a moment's closer examination. The stalk, when extended to the utmost, is an elastic glassy thread, nearly straight, like a wire, but never so absolutely straight as not to show slight undulations. The stalk, when thus drawn tight, is highly sensitive to vibrations in the surrounding medium ; and as in the circumstances in which we observe the animals, such vibrations must be every instant communicated to the vessel in which they are confined, the stalks are no sooner fully extended than they contract with alarm. This depends on a contractile cord which passes throughout the entire length of the stalk, and which is distinctly visible in the larger species as a narrow band. We can scarcely err in considering this ribbon as a rudimentary form of muscle, though we do not recognise in it some of the characteristic conditions which we are accustomed to see in it in higher animals.

The contraction of the muscle is very sudden, energetic, and complete. With a rapidity which the eye cannot follow, the vase is brought down almost to the very base of the stalk. Then it slowly rises again ; and now we see, what we could not discern in the act of contraction itself, that in that act the stalk was thrown into an elegant spiral of many turns, which at the utmost point of contraction were packed close on each other, but which in the extending act gradually separate, and at length straighten their curves.

In any stage of the extension, the sudden contact of the vase with any floating or fixed object apparently causes alarm, and induces the vigorous contraction; but vibrations, even when so violent as those produced by tapping the stage of the microscope with the finger-nail, have no effect unless the stalk be tense, its own power of vibration being then only developed, just as a cord becomes musical in proportion to its tension.

is not until we view these creatures with a good microscope that we acquire an adequate idea of their beauty : for myself, at least, it was so. I had seen engravings of many of the invisible animalcules, and had read technical descriptions ; but of their brilliant transparency, their sudden and sprightly motions, their general elegance and delicacy, and the apparent intelligence with which they are endowed, neither books nor engravings had given me any conception.

Some of the individuals under our present examination are exhibiting phenomena of no less interest than their form and motions. Some of the stalks are terminated by two vases instead of one, which appear to spring from a common point. These, however, are the result of the spontaneous splitting of one; and in other examples you may see the process in different stages ; or, if your patience endure a couple of hours' watching, you may trace the whole phenomena, as I have done, from the moment when it first becomes perceptible, to its completion in the freedom of one of the newly-formed animalcules.

For instance, you perceive that one of the bells instead of being vase-shaped has assumed a globular form. By keeping your eye on this for only a few moments, you detect a depression forming in the midst of its front outline, which momentarily deepens, until it is manifestly a cleft. The division proceeds downwards, the two halves healing simultaneously, so that they are at all times perfectly smooth and rounded; at length two vases appear, side by side, where a few minutes before there had been but one.

One of these is destined to be ultimately thrown off, while the other retains sole possession of the stalk. You soon see which it is that is going to emigrate: for, though the two are alike in size, the roving one early closes the mouth of the vase, becoming smooth and globular there, never to open again. The cilia, now therefore become useless, disappear by absorption ; but meanwhile a new circle of these organs is developed around the basal extremity of the vase, and these, every instant becoming more vigorous in their motions, sway the little globe about on its point of attachment. At length the connexion yields, breaks, and the animalcule shoots away, rowed by its hundred oars, to find a new abode, and to found a new colonv.

Here and there you see shooting through the group, with a rapid gliding movement, an oblong clear body. This is one of the vases, formed by self-division, and exercising its newly-found power of locomotion. It is giddily roving hither and thither, until the instinct of wandering ceases, when it will soberly settle down, affix itself by the point which was formerly its mouth, whence a new stalk will gradually grow, and opening a new mouth in the midst of the new crown of cilia,

I believe that the division is sometimes transverse instead of longitudinal, the cleft occurring by constriction across the middle of the vase; but this I have not seen. In whatever direction it takes place, it is essential that the oblong granular body, called the nucleus, which you see in each vase, be divided, the cleft passing through the middle of this substance, a portion of which is therefore appropriated to each new-made animal.

That the essential vitality of the creature resides in this nucleus is shown by another and highly curious mode of increase, namely, that which is effected by encystion. Let us search the live-box carefully ; for, amidst so great a profusion of Vorticellce as we have on this Nitella, it will go hard if we do not find some individuals in the encysted stage.

Look at this elegant object. It resembles a trumpet of the clearest glass, with a rounded extremity, and with the base affixed to the weed, from which it stands up erect. Within the expanded part of the trumpet there is a turbid mass, with a perfectly defined outline, from several points of which proceed radiating pencils or tufts of long, straight, stiff, elastic filaments, like threads of spun glass, varying greatly in length, and each terminated by a little knob of the same material. The tout ensemble of this object is very attractive and beautiful, and its history is a tale of marvels.

No wonder that Ehrenberg, supposing this form to be

ACIXETA.

an independent animal, gave it a generic and specific name. He called it Acineta mystacina. For who would have suspected that this stiff* and motionless object, with its tufts of flexible but inanimate threads, had any con-

nexion with the sprightly vases which we have been examining 1 Yet it is the same animalcule, in what we may, with a certain liberty of phrase, call its chrysalis condition !

The history of the Vorticella, as it has been elaborately worked out by Dr. Stein, exhibits phenomena analogous to those marvellous changes which we lately considered under the appellation of the Alternation of Generations. Large individuals withdraw their circle of cilia, close up the mouth, and become globular, and then secrete from their whole surface a gummy substance, which hardens into a spherical transparent shell called a cyst, inclosing the Vorticella in its cavity. Within this cyst is seen the hand-shaped nucleus, unchanged, and what was the contractile bladder, which, however, no longer contracts.

By-and-by this torpid Vorticella enlarges itself irregularly, pushing out its substance in tufts of threads, and frequently protruding from one side a larger mass, which becomes an adhering stalk. Thus it has become an Acineta, such as we now behold.

From this condition two widely different results may iproceed. In the one case, the encysted Vorticella separates itself from the walls of the Acineta, contracts into an oval body, furnished at one end with a circle of vibratory cilia, by whose movements it rotates vigorously in its prison, while the more obtuse end is perforated by a mouth leading into an internal cavity. In the interior of this active oval body there are seen the band-like nucleus, and a cavity which has again begun to contract and to expand at regular intervals. It is, in fact, in every respect like a Vorticella vase, which has just freed itself from its stalk. Presently, the perpetual ciliary action so far thins away the walls of the Acineta that they burst at some point or other, and the little Vorticella breaks out of prison, and begins life afresh. The Acineta, meanwhile, soon heals its wound, and after a while develops a new nucleus, which passes through the same stages as I have described, and bursts out, a second Vorticella.

But the cycle of changes may be quite different from this. For sometimes the nucleus within the Acineta, instead of forming a Vorticella, breaks itself up into a great number of tiny clear bodies, resembling Monads, which soon acquire independent motion, and glide rapidly about the cell formed by the inclosed Vorticella-body as in a little sea. But, by-and-by, this body, together with the Acineta wall, suddenly bursts, and the whole group of Monad-like embryos are shot out, to the number of thirty or upwards. The Acineta now collapses and disappears, having done its office, while the embryos shoot hither and thither in newly-acquired freedom. It is assumed, on pretty good grounds, that these embryos soon become fixed, develop stalks, which are at first not contractile, and gradually grow into perfect Vorticellce, small at the beginning, but capable of self-division, and of passing into the Acineta stage, and gradually attaining the full size of the race.

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