The structure of these tentacles is very interesting. The stem contains a core or central chain of large cells, which take a somewhat square outline from mutual pressure. The surface is roughened with small swellings, from each of which projects a long and extremely attenuated hair (palpocil), which is probably a very delicate organ of touch. The terminal sflobe is filled with proportionately large oval vesicles, each with a central cavity, which are arranged in a divergent manner around the centre, so that their tips shall reach the surface of the globe ; these are those potent weapons of offence called thread-cells (cnidce). The surface of the globe is covered with short thick palpocils, which Dr. T. S. Wright considers as prehensile organs. "These papocils arise, each as a somewhat rigid process, from the side of one of the large thread-cells, buried in the head of the tentacle ; and they probably convey an impression, from bodies coming into contact with them, to the thread-cell, causing the extrusion of its duct."

Besides these globe-headed tentacles, there are, on the lower part of the club-foot, four other organs similar in every respect, except that they are not furnished with heads, nor any terminal dilatation whatever. They project horizontally as the knobbed- ones, but their origin, and the respective lines of their radiation, are intermediate or alternate ; in other words, if we consider the

globe-heads as pointing S., and W., the simple ones point N.E, S.E., S.W., and N.W.

From the carefully made observations of several excellent naturalists, as Dujardin, Steenstrup, Dalyell, Loven, and others, it appears that this beautiful and elegant little Polype gives birth to medusa-shaped young. Contrary, however, to the rule in Laomedea, the Medusa is in this case pushed forth as a bud from the side of the club, without any protecting capsule. The process is exceedingly like a plant developing a flower ; for the bud grows until it at length expands blossom-like, and a beautiful little umbrella-form Medusa is seen adhering to the Polype. At length the brilliant little living flower becomes detached; and, after swimming freely for a time, discharges ova or gemmules from its ovaries, which develop into a creeping root-thread, and finally into the club-headed threads of the Stauridia.

Some objects which I have to exhibit to you are altogether unique as to their appearance ; and, if you are not as imperturbable as a Stoic philosopher or a Mohawk Indian, will certainly excite both your risibility and your wonder. For some little time I have been keeping in this tank a specimen of that rather rare and very interesting Sabella, the Amjihitrite vesiculosa of Montagu.* You see it is a worm, inhabiting a sort of skinny tube, much begrimed with mud, about two inches of its length being exposed ; the remainder, or about as much more, being concealed among the sand and sediment of the bottom.

A beautiful object is presented by the gill-fans of this worm. These organs are always elegant, whatever species of the genus is before us; but here, in addition to the charm of the slender filaments, so delicately fringed with their double comb-like rows of cirri, the tip of each bears a dark purple spherule. That of the anterior filament on each side is much larger than the rest, and forms a stout, * "Linn. Trans.," xi. 19.

globose, nearly black ball ; the others diminish to about the twelfth on each side, where they disappear. These balls are placed on the inner or upper face of the filamentstem, at the point where the pectination ceases, the stem itself being continued to a slender point beyond it, and constituting the "short hyaline appendage" of Montagu. From their great resemblance to the tentacle-eyes of the Gasteropod Mollusca, I have little doubt that these are organs of vision. If so, the profusion with which the Sabella is furnished in this respect may account for its excessive vigilance ; which is so great, that not only will the intervention of any substance between it and the light cause it to retire, but very frequently it will dart back into its tube almost as soon as I enter the room, even while I am ten feet distant.

It is not, however, to the tube, nor to the worm, that I wish specially to direct your attention : yet it is necessary that I say a preliminary word about the former. Ordinarily the tubes of these worms are formed of the fine impalpable earthy matters (clay, mud, ifcc), held in suspension in the sea, incorporated with a chitinous secretion from the body of the animal; and therefore the surface of the tube is always rough and opaque. But in this individual case, the water in the vessel, probably owing to its habitual stillness, not holding in suspension the particles of mud that ordinarily enter into the composition of the tube, the latest formed portion is composed of pure transparent cJiitine, without any perceptible earthy element. This clear terminal portion of the tube you may perceive to be occupied by a curious parasite. About twenty bodies, having a most ludicrously-close resemblance to the human figure, and as closely imitating certain human motions, are seen standing erect around the mouth of the tube, now that the Sabella has retired into the interior,, and are incessantly bowing and tossing about their arms in the most energetic manner.

As soon as you have recovered a little from your surprise at this strange display, we will begin to examine the performers more in detail. A slender creeping thread, irregularly crossing and anastomosing, so as to form a loose network of about three meshes in width, surrounds the margin of the Sabella's tube, adhering firmly to its exterior surface, in the chitinous substance of which it seems imbedded. Here and there free buds are given off, especially from the lower edge; while from the upper threads spring the strange forms that have attracted our notice. These are spindle-shaped bodies, about -^th of

an inch in height, whose lower extremities are of no greater thickness than the thread from which they spring ; with a head-like lobe at the summit, separated from the body by a constriction, immediately below which two lengthened arms project in a direction towards the axis of the tube.

Such is the external form of these animals, and their movements are still more extraordinary. The head-lobe of each one moves to and fro freely on the neck, the body sways from side to side, but still more vigorously backward and forward, frequently bending into an arch in either direction; while the long arms are widely expanded,

tossed wildly upward, and then waved downward, as if to mimic the actions of the most tumultuous human passion.

Whenever the Sabella protrudes from its tube, these guardian forms are pushed oat, and remain nearly in contact with the Annelid's body, moving but slightly ; but no sooner does it retire than they begin instantly to bow forward and gesticulate as before. These movements are continued, so far as I have observed, all the time that the Sabella is retracted, and are not in any degree dependent on currents in the surrounding water, whether those currents be produced by the action of the Annelid or by other causes. They are not rhythmical ; each individual appears to be animated by a distinct volition.

Applying a higher magnifying power than we have yet used to the animals, we find that the head-lobe incloses a central cavity ; that the arms are also hollow, with thick walls, marked with transverse lines, indicating flattened cells, and muricated on the exterior ; and that the body contains an undefined somewhat opaque nucleus, doubtless a stomachal cavity.

I cut out, with fine scissors, a segment of the tube, including two of the parasites, with the portion of the network of threads that carried them. They have become immediately paralysed by the division of the threads, but those that remain on the tube are unaffected by the violence. Subjecting one of the animals so cut out to the action of the compressorium, with a power of 560 diameters, the arms are seen to be formed of globose cells, made slightly polyhedral, or many-sided, by mutual pressure, set in single series. The interior of these organs is divided by partitions, placed at intervals of about the diameter. Some at least of the cells contain a small bright eccentric nucleus.

When the tissues were quite crushed down by the pressure of the compressorium, a quivering motion was visible among the disjointed granules, but it was very slight.

trace of cilia, nor any appearance of ciliary motion, was perceptible during life.

When I first discovered these strange beings, I was as much astonished by what I saw as you are ; nor could I imagine to what class of animals they were to be referred. Neither did I know whether their presence on the tube of the worm was a mere accident, or whether it indicated a predominant instinct. On both these points, however, light has been shed.

This larger Sabella tube was not the only one infested with the parasites. I observed them on at least two smaller specimens of the same species, in the same situation, and with precisely the same movements. The extremity of one of those smaller tubes I cut wholly off, and placed in the live-box of the microscope. Two of the parasites only were on it, which were active at first, but in about an hour—probably from the exhaustion of the oxygen in the small quantity of water inclosed—they decomposed, or rather disintegrated, the outline dissolving, and the external cells becoming loose and ragged, and the whole animal losing its definite form.

One of these specimens, however, while yet alive and active, afforded me an observation of value. I had already associated the form conjecturally with the Hydroid Polypes, and was inclined to place it in the family Corynidce, considering the arms to be tentacles, and the headlobe to be homologous with them in character, but abnormal in form. It appeared to be a three-tentacled Coryne, with the tentacles simple instead of having heads. But while I was observing the individual in question, I saw it suddenly open the head-lobe, and unfold it into the form of a broad shovel-shaped expanded disk, not, however, flat, but with the two halves inclining towards each other, like two leaves of a half-opened book. This immediately reminded me of the great sucking-disk which, as I lately told you, I had seen evolved from the obtuse summit of Stauridia producta, and confirmed my suggestion of the natural affinities of the form.

Altogether unlike, in their shape, and in the unwonted vivacity and peculiar human character of their movements, all the other members of their natural family that I had ever seen or heard of, these curious creatures have afforded much entertainment, not only to myself, but to those scientific friends to whom I have had opportunities of exhibiting them. When I see them surrounding the mansion of the Sabella, gazing, as it were, after him as he retreats into his castle, flinging their wild arms over its entrance, and keeping watch with untiring vigilance until he reappears, it seems to require no very vivid fancy to imagine them so many guardian demons ; and the Lares of the old Roman mythology occurring to memory, I described the form under the scientific appellation of Lar Sabellarum. You may, however, if it pleases you better, call them " witches dancing round the charmed pot." *

The Polypes that we have as yet been looking at are all of simple structure individually, though some of them we have seen united into a very populous community of compound life. \Ye will now look at some whose organisation is of a higher, that is, more complex character.

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