From all these observations there cannot remain a doubt of the successive evolution of the entire ecthoreum.

You ask, What is the nature of the force by which the contained thread is expelled'? That it is a potent force is obvious to any one who marks the sudden explosive violence with which the nipple-like end of the cnida gives way, and the contents burst forth ; as also the extreme rapidity with which, ordinarily, the whole length is evolved. A curious example of this force once excited my admiration. The ecthoreum from a cnida of Corynactis viridis was in course of rapid evolution, when the tip came full against the side of another cnida, already emptied. The evolution was momentarily arrested, but the wall of the empty capsule presently was seen to bend inward and suddenly to give way, the ecthoreum forcing itself in, and shooting round and round the interior of the cnida.

sea-anemones: their weapons.

The most careful observations have failed to reveal a lining membrane to the cnida. I have repeatedly discerned a double outline to the walls themselves, the optical expression of their diameter ; but have never detected any, even the least, appearance of any tissue starting from the walls, as the ecthoreum bursts out. My first supposition, reluctantly resigned, was, that some such lining membrane, of high contractile power, lessened, on irritation, the volume of the cavity, and forced out the wire.

The cnida is filled, however, with a fluid. This is very distinctly seen occupying the cavity, when, from any impediment, such as above described, the wire flies out fitfully ; waves, and similar motions, passing from wall to wall. Sometimes, even before any portion of the wire has escaped, the whole mass of tangled coils is seen to move irregularly from side to side, within the capsule, from the operation of some intestine cause. The emission itself is a process of injection ; for I have many times seen floating atoms driven forcibly along the interior of the ecthoreum^ sometimes swiftly, and sometimes more deliberately. Nothing that I have seen would lead me to conclude that the wall of the cnida is ciliated.

I consider, then, that this fluid, holding organic corpuscles in suspension, is endowed with a high degree of expansibility ; that, in the state of repose, it is in a condition of compression, by the inversion of the ectlioreum; and that, on the excitement of a suitable stimulus, it forcibly exerts its expansile power, ecthoreum,—the distending, and, consequently, projecting, the tubular only part of the wall that will yield without actual rupture.

It has been proved that the execution of these weapons is as effectual as their mechanism is elaborate. The wire shot with such force penetrates even to its base the tissues of the living animals which the Anemone attacks ; and then its barbs preclude the withdrawal of the dart. But the entrance of bodies so excessively slender would of itself inflict little injury; there is evidently the infusion at the same time of a highly subtle poison into the wound ; some venomous fluid escaping with the discharge of the ecthoreum, which has the power, at least when augmented by the simultaneous insertion of scores, or hundreds, of the weapons, of suddenly arresting animal vigour and speedily destroying life, even in creatures—fishes, for example—far higher than the Zoophyte in the scale of organisation. I have seen a little fish in perfect health come into accidental contact with one of the acontia of an irritated Sagartia, when all the evidences of distress and agony were instantly manifested ; the little creature darted wildly to and fro, turned over, sank upon the bottom, struggled, flurried, and was dead.

Admitting the existence of a venomous fluid, it is difficult to imagine where it is lodged, and how it is injected. The first thought that occurs to one's mind is, that it is the organic fluid which we have seen to fill the cnida, and to be forced through the everting tubular ecthoreum. Bu t if so, it cannot be ejected through the extremity of the ncthoreum, because if this were an open tube, I do not see how the contraction of the fluid in the cnida could force it to evolve ; the fluid would escape through the still inverted tube. It is j ust possible that the barbs may be tubes opei 1 at the tips, and that the poison-fluid may be ejected through these. But I rather incline to the hypothesis, that the cavity of the ecthoreum, in its primal inverted condition, while it yet remains coiled up in the cnida, is occupied with the potent fluid in question, and that it is poured out gradually within the tissues of the victim, as the evolving tip of the wire penetrates farther and farther into the wound.

I do not think that the whole range of organic existence affords a more wonderful example than this of the minute workmanship and elaboration of the parts ; the extraordinary modes in which certain prescribed ends are attained, and the perfect adaptation of the contrivance to the work which it has to do. We must remember that all this complexity is found in an animal which it is customary to consider as of a very simple structure. But the ways of God are past finding out. These are but parts of His ways.*

The presence of these very remarkable organs is not limited to the Actinoids. They exist in the entire class of Polyps, including the Medusa?, also in the Synaptic (see p. 299 svpra), many Turbellarice, some of the Annelids, and a few among the Mollusca. Dr. R. Bergh of Copenhagen has published (1861) some elaborate researches, proving the existence of urticating cnidse, in abundance, in several forms of the charming Naked-gilled Mollusca, allied to Eolis ; while they seem to be wanting in the tougher-skinned Doris, &c.

Chapter XX. Protozoa and Sponges

We are so accustomed to see certain of the vital functions of animals performed by special organs or tissues, that we wonder when we find creatures which move without limbs, contract without muscles, respire without lungs or gills, and digest without a stomach or intestines. But thus we are taught that the function is independent of the organ, and, as it were, prior to it ; though in nine hundred and ninety-nine cases out of a thousand it be associated with it. In truth, the simplest forms of animal life display very little of that division of labour, the minuteness of which increases as we ascend the organic scale ; the common tissue is not yet differentiated* (to use the awkward term which is becoming fashionable among physiologists) into organs, but it is endowed with the power of fulfilling various oifices, and performing many functions. In all probability, the function is but imperfectly performed; the specialisation of certain tissues, and their union into organs, and the complexity of such combinations, no doubt, perform the given function in a far more complete degree; and it is the number and elaborateness of these that constitute one animal higher in the scale than another. The human lung is no doubt a more complete breathing apparatus than the entire ciliated surface of an Infusory,f and the human eye sees more perfectly than

The term is used to express the cellular development of an organisation from its original germ.

The name given to a class of minute animals from their being generally developed in infusions of animal or vegetable matter.

the loose aggregation of pigment granules on the edge of a Medusa. But this diversity is essential to creation, as the great and wondrous plan which we see it to be ; and, meanwhile, we may rest satisfied that the humble requirements of the lowest organism are met adequately by its humble endowments.

This evening I propose to show you some of these humble conditions of animal life ; the lowest of the lowly. I have here two or three phials of very rich water from the fresh-water ponds in the neighbourhood. All collections of water are not equally productive; and very far indeed is the popular notion from correctness, that every drop of water which we drink contains millions of animalcules. You may find many collections of clear water, springs, streams, and pools, from which you may examine drop after drop in succession, with the highest powers of the microscope, and scarcely discover a solitary animalcule. Again, it is not stagnant and fetid pools that are the richest in vitality ; though no doubt you will always obtain some forms abundantly enough in such conditions. According to my own experience—an experience of many years —the paucity or profusion of animal life in any given collection of water can never be determined beforehand ; the season, the situation, the aspect, the character of the country, and many other ud suspected conditions, influence the result, at which yet one may often give a shrewd guess. Generally speaking, small ponds, in which there is a good deal of vegetation below the surface, and particularly if this be of a minutely divided character, such as Myriophyllum, Chara, &c, and whose surface is well covered with duckweed (Lemna), yield well ; and, in collecting, it is desirable so to dip that some of the fine loose sediment of the bottom may flow into your phial, and then to pluck up one or more of the filamentous water-plants, and introduce these into it.

Now to examine such a collection, proceed as I am about to show you. Hastily glancing with the pocket-lens over the foliage, and selecting such filaments as seem the most loaded with dirty floccose matter, I pluck off with pliers one or two, together with one or two of the cleaner ones that are higher up on the plant, nearer the growing point. Having laid these on the lower glass of the live-box, I take up with the tip of a fine tube, or a pipette, a minute quantity of the water at the bottom, which flows in as you see, carrying a few granules of the sediment. This drop I discharge upon the glass of the live-box, put on the cover, and place the whole on the stage of the microscope.

First, let us use a low power, one hundred diameters or so, in order to take a general glance at what we have got. Here is an array of life, indeed ! Motion arrests the eye everywhere. " The glittering swift and the flabby slow" are alike here; clear crystal globules revolve giddily on their axes ; tiny points leap hither and thither like nimble fleas ; long forms are twisting to and fro ; busy little creatures are regularly quartering the huntingground, grubbing with an earnest devotedness amoncr the sediment as they march up the stems; here are vases with translucent bodies protruding from the mouths; here are beauteous bells, set at the end of tall threads, ever lengthening and shortening ; here are maelstroms in miniature, and tempests in far less than a teapot ; rival and conflicting currents are whirling round and round, and making a series of concentric circles among the granules. Surely here is material for our study.

I see an object slowly creeping along the glass, which will be just the thing for our purpose. It is the Proteus {Amoeba diffluens)* Let me put on a higher power, and submit it to your observation.

The names given to this little creature are expressive of its character. Amoeba is from the Greek a/ictj3t) (amoibe), signifying change ; and Proteus in mythology was an old prophet of the sea, who when seized assumed all manner of forms to avoid uttering his predictions.

You see a flat area of clear jelly, of very irregular form, with sinuosities and jutting points, like the outline of some island in a map. A great number of minute blackish granules and vesicles occupy the central part, but the edges are clear and colourless. A large bladder is seen near one side, which appears filled with a subtle fluid.

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