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.

You will have observed that the admixture of carmine to the water, while the animalcules were active, shows the direction of the ciliary motion with great distinctness. The particles form two eddies, one on each side of the front, which meet in the centre in a strong current, and pass off behind the mouth on each side. We do not perceive that any of them swallow the particles of carmine, for the internal vessels remain colourless.

I have found that if a drop of water containing these animals be placed on a slip of glass exposed to the open air, they do not burst as the water dries away, but dry flat on the glass, their bodies broader but shorter than when alive, and quite entire. Their cilia are then very manifest. On being again wetted, though after only a few minutes' desiccation, I have never been able to revive them, nor any other Infusoria in like circumstances, notwithstanding what is stated in books.

Here is another species in equally amazing profusion, S. mytilus. Its form is oblong, with rounded extremities, the anterior obliquely dilated. This species affords a good example of the various organs of locomotion. A transparent oblong shield, which is quite soft and flexible, is spread over the back, which does not prevent our eyes discerning all the organs through it ; though, much more commonly, the animal, when under the microscope, crawls, belly upward, beneath the glass cover of the live-box. Around the anterior part, which is broadened, are placed cilia, which are vibratile ; these are continued round the mouth, a sort of fold on the side. Towards the posterior extremity on each side are other rows of cilia, which beinglarge are well displayed. On the ventral surface, chiefly towards the front part, are seen several thick pointed processes, shaped like the prickles of a rose, but flexible, and capable of being turned every way. These are the ttncini, and are evidently used as feet, the tips being applied to the glass. The optical effect of the throwing about of these uncini, when the place which they touch is in focus, is very curious. They are rapidly moved, but without regularity ; the tips bend as they touch the surface of the glass ; some of them seem to have accessory hairs, equally long, but slender, proceeding from the same base. On the hinder quarter of the ventral surface are several thick pointed spines; these are inflexible, nearly straight, placed side by side, but not in regular order, some reaching beyond others. I have not seen these used, but they commonly remain sticking out in a horizontal direction. These organs are termed styles. Besides these, there are three slender bristles, called setce, placed at the hinder extremity, the central one in the line of the body, the others radiating at an angle. These are distinguished from the cilia, not only by their length, but by not being vibratile. The motions of these animals are powerful, but, irregular and fitful, very much like those of the former species. They dart hither and thither, backward as well as forward, occasionally shooting round and round in a circle, with many gyrations, much like the pretty little polished bettles (Gyrinus) that play in mazy dances on the surface of a pool. The two extremities seem covered with minute pits or stipplings, but colourless ; the central part is occupied with yellowish granules of different sizes.

I once witnessed the dissolution of one of these animals under peculiar circumstances. Two or three stems of an aquatic plant had become crossed in the live-box so as to form an area, into which the Stylonychia had somehow introduced himself. There was just room for him to move backward and forward without turning, and the space was about three times his own length. Within this narrow limit he impatiently continued crawling to and fro, moving his uncini with great rapidity, and showing their extreme flexibility ; for, as he applied them now to the stem, now to the surface of the glass, these whip-like uncini were sometimes bent double. The so-called styles at the posterior extremity, though less frequently used so, were yet occasionally bent and applied to the surface as feet, so that they are certainly not inflexible as supposed, nor do I see any essential difference between them and the uncini. The whole body was flexible, taking the form of any passage or nook into which it was thrust, yet recovering its elasticity immediately the pressure was removed. Its proper form appeared to be convex above and concave beneath, rather than flat. After having been thus employed about half an hour under my observation, it became still, moving only its cilia, when I left it a little while, and on my return found that it was dissolved ; the outline having entirely disappeared, and nothing being left but the granules, and globular vesicles, that had constituted its viscera, some of which still contained the carmine which had been very perceptible in the living animal. This was the more remarkable, as there was plenty of water. It looked like suicide,— a spontaneous choosing of death rather than hopeless captivity.

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