The next form of these organs is the Tangled Cnida. This form is very generally distributed, and is mingled with the former in the various tissues. In the genus Sagartia, however, it is by far the rarer form, while in Actinia and Anthea it seems to be the only one.

The pretty little Corynactis viridis is the best species that I am acquainted with for studying this kind of cnida- . A fragment of its craspeda I have here ready for your observation, prepared exactly like that of C. Smithii. The figure of the cnidce is nearly that of a perfect oval, but a little flattened in one aspect, about -^o^h °^ an inch in the longer, and y^th in the shorter diameter. Their size, therefore, makes them peculiarly suitable for observations on the structure and functions of these curious organs. Within the cavity lies a thread (ecthoreum) of great length and tenuity, coiled up in some instances with an approach to regularity, but much more commonly in loose contortions, like an end of thread rudely rolled into a bundle with the fingers.

The armour of this kind does not differ essentially 2 B from that already described. It is true I have detected it only in Corynactis, where the short ectkoreum of the Tangled Cnida is surrounded throughout its length by a barbed strebla of three bands. The barbs are visible, under very favourable conditions for observation, even while the tangled wire remains inclosed in the cnida, but their optical expression is that of serratures of the walls, without the least appearance of a screw. This, I say, is the only species in which I have actually seen the armature of the ectkoreum in this kind of cnidce ; but I infer its existence from analogy in other species, where the conditions that can be recognised agree with those in this, though the excessive attenuation of the parts precludes actual observation of the structure in question. Spiral Cnidse constitute the third form.* In a few species, as Sagartia parasitica, Tealia crassicor/iis, and CeriantJms membranaceus, I have found very elongated fusiform cnida 1 , which seem composed of a slender cylindrical thread, coiled into a very close and regular spiral. In some cases the extremities are obtuse, but in others, as in T. crassicornis, an

CNIDA OF CORYXACTIS. example of which I now show you, the posterior extremity runs off to a finely-attenuated point, the whole of the spire visible even to the last ; the whole bearing no small resemblance to a multispiral shell, such as one of the Cerithiadce or Twrritelladae. The ecthoreum is discharged reluctantly from this form, and I have never seen an example in which

Dr. Karl Mobiiss (Abhandl. Naturw. Yer. z. Hamburg, 1866), considers this to be only an immature condition.— P. H. G., 1884.

sea-anemones: their weapons. the Mrhole had been run off. So exceedingly subtle are the walls of the cnidce, that it was not until after many observations that I detected them ; in an example from T. crassicornis, which had discharged about half of the wire, I could not see the slightest sign of armature on the ecthoreum. So far as my investigations go, these Spiral Cnidse are confined to the walls of the tentacles, in which, however, they are the dominant form.*

Such, then, are the form and armour of these organs. But I have not yet done with them. The emission of the wire, strange to say, is a process of distinct evolution, or expansion from within, from beginning to end. The ecthoreum is not a solid, but a tubular, prolongation of the walls of the cnida, turned-in, in its first condition ,. like the finger of a glove drawn inwards. Of this fact you may convince yourself by a careful watching of the phenomena before you. Many of the ecthorea from the tangled cnidce now under your eye run out, not in a direct line, but in a spiral direction. Select one of these, and you w T ill perceive that each bend of the spire is made, and stereotyped, so to speak, in succession, while the tips go on lengthening ; the tip alone progresses, the whole of the portion actually discharged remaining perfectly fixed ; which could not be on any other supposition than that of evolution.

In the discharge of the chambered kind (to revert to those which we were just now examining) we saw the ventricose basal part first appear ; the lower barbs flew out before the upper ones, and all were fully expanded before the attenuated portion began to lengthen. This, again, is consistent only with the fact of the evolution of the whole. On several occasions of observation on the chambered cnidce of C. Smithii, I have actually seen the unevolved portion of the ecthoreum running out through

These details, with many others, are given in my Hist, of Brit. Sea-anemones and Corals, Introd., xxii—xl. o P o the centre of the evolved ventricose portion. But perhaps the most instructive and convincing example of all was the following. One of the large tangled cnidce of Cori/nactis viridis had shot about half of its wire with rapidity, when a kind of twist, or "kink," occurred against the nipple of the cnida, whereby the process was suddenly arrested. The projectile force, however, continuing, caused the impediment to yield, and minute portions of the thread flew out piecemeal, by fits and starts. By turning the stage-screw, I brought the extremity of the discharged portion into view, and saw it slowly evolving, a little at a time. Turning back to the cnida, I saw the kink gradually give way, and the whole of the tangled wire quickly flew out through the nipple. I once more moved the stage, following up the ecthoreum, and presently found the true extremity, and a large portion of the wire, still inverted ; slowly evolving, indeed, but very distinct throughout its whole course, within the walls of the evolved portion.

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.

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