Look at thisbeautiful Scarlet-fringedAnemone (Sagartia miniata), expanding to the utmost its disk and tentacles in the clear water of the tank. I touch its body; instantly the blossom-like display is withdrawn: the column closing over it in the form of a hemispherical button, which goes on contracting spasmodically. At the same time see these white threads which shoot out from various points of the surface; new ones appearing at every fresh contraction, and streaming out to a length of several inches, resembling in appearance fine sewing cotton twisted and tangled irregularly.

Now the animal has attained its utmost contraction, and the threads lengthen no more. But already they are disappearing ; each is returning into the body by the orifice at which it issued. It is, as you may see by examining it carefully with a lens, gradually contracting into small irregular coils, at that end which is attached to the animal ; and these little coils are, one after the other, sucked in, as it were, through an imperceptible orifice.

Before the whole have disappeared, we will secure a portion for examination. For this purpose I cut off with sharp scissors about one-sixth of an inch of the extremity of one of the threads, which now I transfer to a drop of sea-water in the compressorium. These threads are called acontia.

Examining this fragment under a low power of the microscope, we readily see that, though at first it seems a solid cylinder, it is really a flat narrow ribbon with the edges curved-in, which can at pleasure be brought into contact, and thus constitute a tube. Like all other internal organs in these animals, its surface is richly ciliated, and the ciliary currents not only hurl along whatever floating atoms chance to approach the surface, but cause the detached fragments themselves to wheel round and round, and to swim away through the water. Though there is not the slightest trace of fibre in the structure of the acontiwni) when examined even with a power of eight hundred diameters, the clear jelly, or sarcode, of which

POEIIOX OF ACONTIUH (flattened). its basis is composed, is endowed with a very evident contractility ; the filament can contract or elongate ; can extend itself in a straight line, or throw its length into spiral curves and contorted coils ; can bring its margins together, or separate them in various degrees ; can perform the one operation at one part, and the other at another, and thus can enlarge or attenuate the general diameter of the cord, apparently at will. Some of these changes can be effected even in the fragment detached

from the animal ; thus proving that the moving power, whatever it is, is situated in the constituent tissue itself.

Under pressure the edges of the flattened acontium appear to be thronged with clear viscous globules, overlapping one another, and protruding ; indicating one or more layers of superficial cells, doubtless forming the epithelium.* As the pressure is increased, these oozr out as long pear-shaped drops, and immediately assume a perfectly globular form, with a highly refractive power. Below these is packed a dense crowd of cnidce, arranged transversely.

Before we proceed to the examination of these curious organs in detail, it may be well to devote a moment's attention to the mechanism by which the acontia themselves, are projected from the body. As this was first described (so far as I am aware) by myself, t I will take the liberty of citing some of my observations on the matter. The omission of the acontia is provided -for by the existence of special orifices, which I term cinclides. The integu- |(v ment of the body, in the Sagartice, is perforated by minute foramina, having a resemblance in appearance to the spiracuht of Insects. They occur in the CINCLIDES. interseptal spaces ; opening a communication between these

The thin, delicate cuticle or skin which covers all the free, uninclosed, internal surfaces of the body.

t In a memoir, entitled "Researches on the Poison Apparatus in the Actiniadtc," read before the Royal Society, Feb. 4th, 1858.

(and therefore the general visceral cavity) and the external water. It follows that they are placed in perpendicular rows ; but I have not been able to trace any other regularity in their arrangement. So far as I have seen, they are so scattered, that one, two, or even more contiguous intersepts may be quite destitute of a cinclis. I would not, however, attach too much weight to this negative evidence, since the animal has the power of closing them individually at will, and that so completely, that the most careful scrutiny does not detect their presence.

Perhaps the best mode of examining them is to put a small specimen of the S. dianthus or>S'. bell is into a narrow parallel-sided glass cell, tilled with sea-water. After a while the animal will be much distended; the exhaustion of the oxygen impelling the Anemone to bathe its organs with as large a quantity of the fluid as it can inhale. The pellucidity of all the integuments will be thus greatly increased. A strong lamp-light being now reflected by means of the mirror through the animal on the stage of the microscope, an inch or a half-inch objectglass will probably reveal the orifices iu question with much distinctness.

The appearance of the cinclides may be compared to that which would be presented by the lids of the human eye, supposing these to be reversed ; the convexity being inwards. Each is an oval depression, with a transverse slit across the middle. When closed, this slit may sometimes be discerned merely as a dark line—the optical expression of the contact of the two edges ; but, when slightly opened, a brilliant line of light allows the passage of the rays from the lamp to the beholder. From this condition the lids may separate in various degrees, until they are retracted to the margin of the oval pit, and the whole orifice is open.

The dimensions of the cinclides vary not only with the species, and probably also with the size of the individual, but with the state of the muscular contraction of the integument, as, also, I think, with the pleasure of the animal. In a small specimen of S. dianthus, I found the width of a cinclis, measured transversely, yfyth of an inch ; but that of another, in the same animal, was more than twice as great, viz., y^yth of an inch. This was on the thickened marginal ring, or parapet, which in this species surrounds the tentacles, where the cinclides are larger than elsewhere. Watching a specimen of S. nivea under the microscope, I saw a cinclis begin to open, and gradually expand till it was almost circular in outline, and -^^th of an inch in diameter. I slightly touched the animal, and in an instant it enlarged the aperture to y^th of an inch. In a specimen of & bellis, less than half-grown, I found the cinclides numerous, and sufficiently easy of detection, but rather less defined than in dianthus or nivea. They occurred at about every fourth intersept, three intersepts being blind for each perforate one; and about three or four in linear series, but not quite regularly in either of these respects. In this case they were about -~^th. of an inch in transverse diameter—a large size ; and I measured one which was even -g^th of an inch. By bringing the animal before the window, I could discern the light through the tiny orifices with my naked eye.

From several good observations, and especially from one on a cinclis, widely opened, that happened to be close to the edge of the parapet of a dianthus, I perceived that the passage is not absolutely open, at least in ordinary; but that an exceedingly thin film lies across it. By delicate focussing, I have detected repeatedly, in different degrees of expansion, and even at the widest, the granulations of a membrane of extreme tenuity, and one or two scattered cnidw, across the bright interval. On another occasion, in the case of a cinclis at the edge of the parapet, a position singularly favourable for observation, I saw that this subtle film was gradually pushed out until it assumed the form of a hemispherical bladder, in which state it remained as long as I looked at it. At the same time the outline of the cinclis itself was sharp and clear, when brought into focus further in. The film, whatever it be, is superficial, and does not appear to be a portion of the integument proper. I take it to be a film of mucus (composed of deorganised epithelial cells), which is constantly in process of being sloughed from all the superficial tissues in this tribe of animals, and which continues tenaciously to invest their bodies, until, corrugated by the successive contractions of the animal, it is washed away by the motions of the waves. As, however, one film is no sooner removed than another begins to form, one would always expect external pores so minute as these to be veiled by a mucus-film in seasons of rest.

The pressure of this film is sufficient evidence that the cinclides are not excretory orifices for the outflow of the respired water in the manner of the discharging siphon in the Bivalve Mollusca :— at least that no current constantly, or even ordinarily, passes through them. I have watched them continuously for periods sufficient to detect such discharge if it were periodic. On one occasion (viz., that in which the film was protruded like a blown bladder) a minute Infusorial animalcule chanced to pass across, close to the surface of the film : this would have been a decisive test of the existence of a ciliary current ; but not the slightest deviation in the little atom's course could be detected.

That the cinclides are the special orifices through which those missile weapons, the acontia, are shot and recovered, rests not merely on the probability that arises from the co-existence of the two series of facts I have above recorded, but upon actual observation. In a rather large S. dianthus, somewhat distended, placed in a glass vessel between my eye and the sun, I saw, with great distinctness, by the aid of a pocket-lens, many acontia protruded from the cinclides, and many more of the latter widely open. The acontia, in some cases, did not so accurately fill the orifice but that a line of bright light (or of darkness, according as the sun was exactly opposite or not) was seen partially bordering the issue of tinthread, while the thickened rim of the cinclis surrounded all.

The appearance of the orifices whence the acontia issued was that of a tubercle or wart, and the same appearance I have repeatedly marked in examples observed on the stage of the microscope ; namely, that of a perforate pimple, or short columnar tube. This was clearly manifest when the animal, slowly swaying to and fro, brought the sides of the cinclis into partial perspective.

On another occasion I witnessed the actual issue of the acontia from the cinclides. I was watching, under a low power of the microscope, a specimen of a S. nivea, while, by touching its body rudely, I provoked it to emit its missile filaments. Presently they burst out with force, not all at once, but some here and there, then more, and yet more, on the repeated contractions of the corrugating walls of the body. Occasionally, the free extremity of a filament would appear, but more frequently the bight ofa bent one ; and very often I saw two, arid even three, issue from the same cinclis. The successive contractions of the animal under irritation, caused the acontia already protruded to lengthen with each fresh impetus, the bights still streaming out in long loops, till perhaps the free end would be liberated, and it would be a loop no longer ; and sometimes a new thread would shoot from a cinclis, whence one or two long ones were stretching already : while, as often, the new-comers would force open new cinclides for themselves. The suddenness and explosive force with which they burst out, appeared to indicate a resistance which was at length overcome :—perhaps (in part at least) due to the epithelial film above mentioned, or to an actual epiderm,* which, though often ruptured, has ever, with the aptitude to heal common to these lowly structures, the power of quickly uniting again.

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