But while you gaze on it, you perceive that its form is changing : that it is not at two successive moments of exactly the same shape. This individual, which when you first looked at it was not unlike England in outline, is now, though only a few minutes have passed, something totally different; the projecting angle that represented Cornwall is become rounded and more perpendicular; the broken corner that we might have called Kent has formed two little points up in the position of Lincolnshire; the large bladder, which was in the place of the Eastern counties, is moved up to the Durham coast, and is, moreover, greatly diminished ; and other like changes have taken place in other parts.

Lo ! even while speaking of these alterations, they have been proceeding, so that another and a totally diverse out-

FOKMS OF AMCEBA.

Successively drawn from one individual . line is now presented. A great excavation takes the place of Dorset ; Kent is immensely prolonged ; the bladder has quite disappeared, &0.; but it is impossible to follow these changes, which are ever going on without a moment's

intermission, and without the slightest recognisable rule or order. The projections are obliterated or exaggerated ; the sinuosities are smoothed, or deepened into gulfs, or protruded into promontories ; firths form here, capes there; but not by starts, but evenly, and with sufficient rapidity to be appreciable to the eye while under actual observation; though the alterations are more striking if you take your eye off the object for a few seconds, and then look again ; and still more so if you try to sketch the outline. Individuals vary greatly in dimensions; this specimen is about one hundred and twentieth of an inch in long diameter, but others I have seen not more than one-tenth as large as this, and some twice as large.

Disregarding now this peculiarity of change of form, which has procured for it the name of the old sea-god that was so difficult to bind, we will concentrate our attention on some other points not less interesting. That great bladder undergoes changes besides those gradual alterations of place which are dependent on the general form. It slowly but manifestly increases in size up to a certain extent, when it rather suddenly diminishes to a point, and immediately begins to fill again, as slowly as before. These alternations go on with some regularity, and we cannot observe them without becoming convinced that it is a process of filling and emptying; that the bladder gradually fills with a fluid which is either secreted by its walls or percolates into it from the surrounding tissue ; which fluid, when full, the bladder discharges by a sudden contraction of its outline. But whither the fluid goes it is difficult to determine ; I have never been able, in this or in any other instance of its occurrence (though this contractile bladder is characteristic of the extensive classes Infusoria and Rotifera) to see any issue of fluid from the bodyatthe moment of contraction; and therefore conclude that it is discharged into the body, perhaps back again into the tissues from whence it was taken up, and from whence it was about to be collected again. Hence it is probably the first obscure rudiment of a circulation ; the lluids impregnated with the products of digestion being thus collected, and then diffused throughout the soft and yielding tissues.

The smaller bladder-like spaces that you see in considerable numbers in the substance of the animal, are collections of fluid contained in excavations of that substance, which are called vacuoles, differing from vesicles, inasmuch as they seem to have no proper wall or inclosing membrane, but to be merely casual separations of the common substance, such as would be made by drops of water in oil. These vacuoles appear to be connected with the digestive function ; for very many of them are not clear, but are occupied with granules more or less opaque, and of exceedingly various dimensions. That these collections of granules are food you will see by the following experiment.

I mingle a little carmine with the water, just enough to impart a visible tinge to it, and close the live-box again. Already you perceive that some of the tiny globules are become turbid and red, and that their opacity and colour are deepening perceptibly. We see by this that the particles of carmine have been taken into the jelly-like sarcode, and are accumulating in little pellets surrounded by fluids, in these casual hollows of its substance. The process is rendered still more obvious when, as is often the case, some Diatomacean,* with a hard siliceous shell, becomes the food of the Amoeba. The apparently helpless jelly spreads itself over the organism, so as soon to envelop it; the flesh, which, having no skin, can unite with itself whenever the parts come into contact, closes over the

The Diatomacece, a term formed from the Greek cia (dia), through, and rkfivtiv (temneio), to cut, are so called from the ease with which their masses may be broken or cut through ; whence their popular name of brittle-worts. They are usually considered to belong to the vegetable kingdom.

Diatom, which is thus brought into the midst of the sarcode, a vacuole being new-made for its reception. This, then, performs the part of a temporary stomach : the digestible portions of the prey are extracted, and then the insoluble shell of flint is, as it were, gradually squeezed to some part of the exterior, and gradually forced out, the vacuole disappearing with it, or perhaps retaining a minute portion of the fluid, and thus perpetuating itself for a while. This is the earliest condition in which the process of digestion can be recognised.

Another genus somewhat similar is Arcella, but it differs in being furnished with a more or less rounded shell (lorica), like a little box. In examining the matters that adhere to the stems of duckweed, and other water-plants, we frequently observe little circular bodies of a yellowish or reddish-brown colour, some much darker than others, but all having a central round spot paler than the rest. On first examination they seem inert and dead, but if we closely watch one, we perceive that it is endowed with the power of motion ; and we directly discern, thrust out from its edge, variable processes, in the form of arms, of clear, perfectly colourless, and most delicate jelly, sometimes pointed, sometimes blunt, which slowly change their form and position. By the aid of these, a feeble and irregular motion is given to the box, which is sometimes turned partly over; when we perceive that its under side is flat, or probably concave, and that its outline is cut into facets. The lorica is somewhat flexible, for the edges at two opposite points are sometimes bent down towards each other, so as to give the creature the form of a crescent. The internal viscera are dimly discernible through the coloured lorica, and resemble those of Amoeba. A dark oval ring is commonly seen at one side, which is probably the outline of the contractile bladder. It may, in fact, be considered as an Amoeba, whose external surface has the power of secreting a symmetrical shell of horny or chitinous substance. The lorica is about T * ^th of an inch in diameter. This species is named Arcella vulgaris.

Laying aside our live-box with its contents for the present, we will have recourse to the tanks of sea-water for one or two other objects of intermediate interest. On the green and brown mossy sea-weed which covers the rocks on the bottom, you see many white specks clinging to the filaments; and there are several adhering to the sides of the tank. These are little living shelled animals of the class Iforaminifera, and these which you see include several species. By bringing your eye, assisted by the lens, to bear upon one of these latter, you perceive that it is a little discoid spiral shell, of very elegant form, marked with curved diverging grooves. This is the pretty little Pobjstomella crispa, a fair sample of its class, and though not more than -g^th of an inch in diameter, it is a giant compared with the Arcella.

There is more, however, than the shell to be seen ; though so filmy and shadowy, that I wonder not at your overlooking it. Extending from two opposite sides of the shell to a distance each way considerably exceeding its diameter, you discern fine threads of clear jelly, running out in long points. The power you employ is not sufficient to enable you to resolve their detail : and for this I will try to secure a specimen for the microscope.

In this other live-box, then, I inclose one of the white specks from the moss-like clothing of the stones. It is, I see, of another species, namely, Pohjmorphina oblonga; but it will answer our purpose equally well.

At present we see only the shell, the removal of the animal having induced it in alarm to withdraw the whole of its softer parts within the protection of its castle. We must have a few minutes' patience.

Now look again. From the sides of the opaque shell we see protruding tiny points of the clear sarcode; these gradually and slowly,—so gradually and slowly that the eye cannot recognise the process of extension—stretch and extend their lines and films of delicate jelly, till at length they have stretched right across the field of view. The extension is principally in two opposite directions, corresponding to the long axis of the shell; though the branched and variously connected films often diverge considerably to either side of these lines, giving to the whole a more or less fan-shaped figure.

These films are as irregular in their forms and sizes as the expansion of the sarcocle of Amoeba, with which they have the closest affinity. Their only peculiarity is their tendency to run out into long ribbons or attenuated threads, which, however, coalesce and unite whenever they come into mutual contact, and thus we see the threads branching and anastomosing with the utmost irregularity, usually with broad triangular films at the points of divergence and union.

There can be no doubt that the object of these lengthened films, which are termedpsevAopodia* is the capture of prey or food of some kind ; perhaps the more sluggish forms of minute animalcules, or the simpler plants. These the films of sarcode probably entangle, surround, and drag into the chambers of the shell, digesting their softer parts in temporary vacuoles, and then casting out the more solid remains, just as the Amoeba does.

Though this beautiful array was so very deliberately put forth, it is, as you perceive, very rapidly withdrawn on any disturbance to the animal, as when we agitate the water by slightly moving or turning the cover of the livebox. Another fact, of which you may convince yourself, by watching manifest, though small, changes of position in the shell, while under observation, is, that it is by means of the adhesion and contraction of the jiseitdopodia, that the animal drags itself along a fixed surface. This

Literally, false feet, from the Greek iptudog (pseudos), a falsehood, and ttovq (pous), genitive 7rodoQ (podos), afoot.

it can effect so assiduously, that I frequently find them in the morning adhering to the tank-sides three or four inches from the bottom, though, on the previous evening, none were visible on the glass. Thus they must crawl, on occasion, from a hundred to a hundred and fifty times their own diameter in a night.

The structure of a Sponge is much the same as that of these animals, with the exception that its solid part or skeleton is not a continuous covering by which the sarcode is invested, but consists of fibres or points or rods of varying form, which are clothed with the sarcode. This loose sort of skeleton may be of horny or chitinous matter, like that of Arcella, or calcareous like that of theForaminiferdt* or it may be siliceous,—that is, composed of flint (silex).

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