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.

Some forms of the same family, Vorticellada>, are interesting as dwelling in beautiful crystalline houses, of various shapes, always elegant. All these have been ascertained to pass through the same or similar A cineta stages. Cothumia imberbis is one of the prettiest of these. The cell is of an elegant ampulla-like form, perfectly transparent and colourless, set on a stiff foot, or short pedicle, which shows many transverse folds, like those of leather. From the mouth of the vase projects the animal, whose form may be distinctly traced through the clear walls of the cell attached to its bottom, whence it stretches upward when seeking prey, or to which it shrinks when alarmed.

In the former condition the body resembles a much elongated Vorticella, with a similar circular orifice, set round with cilia. Often the animal performs its ciliary vibrations within the shelter of its house, not venturing to protrude beyond its rim. If carmine has been mixed with the water, the atoms are seen in the customary vortex, and some are occasionally drawn into the cell nearly half-way down its cavity, and then swiftly driven out again. On a slight tap upon the table the animal withdraws, and in the same moment the urn bends clown upon its leathery pedicle, at a point w^here there is always an angle, until the rim of the cell is in contact with the plant to which it is attached. This action is instantaneous. Presently, however, it rises, and resumes its former position, and then the mouth of the cell slowly opens, and the animal again protrudes, the cilia appearing first, and finally the head or front part of the animal, which is then opened and begins to rotate.

Very similar to this are the Vaginicolce, but the cells which they inhabit are not stalked, but are immovably affixed to plants. In V. crystalline^ the cell is a tall

VAGI-MCOLA.

goblet, standing erect, perfectly colourless ; while in V. decumbens, it is slipper-shaped, attached along its sides, and of a golden-brown hue, but still quite transparent. Here is, fortunately, a group of the latter species, scattered about the leaves of the Xitella.

Though, in general, both in form and habits, closely

like the Cothurnia, yet the Vaginicola has some peculiarities of interest. The cilia are more developed, and can be more distinctly seen than in either Cothurnia or Vorticella, forming, when in swift action, a filmy ring above the margin, along which, as if upon a wheel, one or more dark points are frequently seen to run swiftly round : the optical expression, as I presume, of a momentary slackening in the speed of the wave. The act of self- division takes place in this animal, as in the Vorticella; and it is curious to see two Vaginicoke, exactly alike, lovingly inhabiting the same cell. One of the cells which we are now examining is in this doublytenanted condition.

I will now exhibit to you some examples of the most highly-organised forms of this class of animals, in which we discern a marked superiority over any that we have yet looked at, and a distinct approach to those animals whose more precise movements are performed by means of special limbs. These creatures are very common, both in fresh and sea water, wherever vegetable matter is in process of decomposition; and hence their presence can at all times be commanded by keeping infusions. In this old infusion of sage leaves, for instance, they occur in vast multitudes, past all imagination, as you may see with a lens in this drop.

This group belongs to the genus Stylonychia, and, as I believe, to the species S. pustulata. It presents the form of an oval disk, which, when seen sidewise, is found to be flat beneath and convex above. It commonly swims with the belly upwards, and, when exhibited on the stage of the microscope, in almost every case, this surface is presented to the eye. It darts about very irregularly, with a bobbing motion, rarely going far in one direction, but shooting a little distance, and then instantly receding, turning short round, and starting hither and thither, so fitfully that it is very difficult to obtain a fair sight of its MICltOSCOPE. structure. Its margin, however, is surrounded by short cilia; the mouth, which is a long opening on the front part, and at the left side (as to the animal) of the ventral surface, is fringed with long cilia, which are continually vibrating. These are the organs of the darting motion; but the creature crawls, like a mouse, along the stems of conferva, Szc, which it performs by means of curved spines, called uncini, near the front part, the points of which are applied to the stem, and also by long stiff styles or bristles, which project backward and downward from the hinder part. Sometimes the animalcules crawl for a moment back downward on the inner surface of the glass cover, when the bases of the anterior curved spines appear dilated like large spots. The spines are not capable of much action, but they are rapidly used. The general appearance of the creature reminds us of the little Woodlouse or Armadillo of our gardens. The interior of the body is occupied with a granular substance, in which are scattered many globular vesicles of different sizes. The animal is very transparent, and almost colourless. They increase very fast by transverse division, which is performed under the microscope, so as greatly to increase the number under examination, even in an hour or two. A constriction forms in the middle of one, which quickly deepens, dividing the oblong creature into two of circular iigure. The mouth of the new one, with its vibratile cilia, is formed long before separation is complete, and at the same end and side as in the parent. The styles and bristles then form, and the creatures are held together for a few seconds by these organs, even when the bodies are distinctly severed. When separated, they retain the round form for some time.

When a drop of such water is examined between two plates of glass, it is amusing to observe the numbers that congregate in the little pools left by the gradual drying of the fluid. This probably becomes unlit for respiration for the motion of the cilia becomes more and more languid, and the creatures die before the water is dry. They not only die,hutva?iish ; so that,—where there were scores, so close that in moving they indented each other's sides and crawled over one another,—if we look away for a few minutes, and again look, we see nothing but a few loose granules. This puzzled me, till I watched some dying, and I found that each one burst and, as it were, dissolved. The cilia moved up to the very last moment, especially the strong ones in front, until, from some point in the outline, the edge became invisible, and immediately the animal became shapeless, and from the part which had dissolved the interior parts seemed to escape, or rather the skin, so to speak, seemed to dissolve, leaving only the loose viscera. From the midst of these then pressed, as if by the force of an elastic fluid within, several vesicles of a pearly appearance, varying in number and size, and then the whole became evanescent.

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