which subsists between the different parts. The singular spinous skeleton; the expanded membrane of the polypary, with its beautiful internal network of tubes and delicate peripheric prolongations; the alimentary polypes, some white and filiform, others thick, fleshy, crimsoD, or yellow sacs, obligingly everted, to expose their interior to our microscopic eye : the reproductive polypes, with their richly coloured generative sacs ; the sessile generative organs of the polypary; the ophidian polypes, coiled in neat spirals when at rest, but starting into furious action, like a row of well-drilled soldiers, when injury is inflicted on the body to which they are attached; and lastly the tentacle polypes, floating in the water like long and slender threads of gossamer, or dragging up heavy loads of food for the common good;—these, together with the intimate relation and sympathy subsisting between the polypary and its associated organs, all combine to form an object of the highest interest, and indicate that, in this fixed yet travelling zoophyte, we have a type of structure transitional between the dentritic Hydroidce and the more highly organised Acaleph* In the simplest acalephoid form, such as the medusoid of Comjianularia [or Laomedeaj (which is nothing more than an extension of the polypary specially organised for independent and motile life), we have (as in Hydractinia) an expanded polypary, represented by the umbrella, and permeated by vascular tubes, from the confluence of which last spring, at the centre, the tenticular polypes, various in number; and between them the reproductive polypes, represented by the sessile generative sacs."f

You see here a jar, on the glass side of which are traced a number of very fine white lines, barely discernible by

From the Greek aicaXiifyr) (akalephe), a nettle, applied to animal known under the common name of •jelly-fishes and sea-nettles, from their causing the sensation of stinging when handled.

f Dr. Wright, op. cit. z 2 the unassisted eye. But by the aid of the lens you see that each line is a long and slender thread, which creeps along the glass, and at length starts out from it free for a short distance, and is then terminated by a long clubshaped body, which carries at its extremity four horizontally divergent organs, like the arms of a turnstile. Tracing down the threads to their lower extremities, you see that they are branches of one thread, which creeps irregularly over a filamentous sea-weed growing from a stone in the jar. The sea-weed had been in the vessel for several weeks, and the water having been undisturbed, the knobbed thread, which was originally confined to the plant, continued to grow, and, coming in contact with the glass, spread upon it. Many other threads have extended from the creeping root, some of which stand up freely in the water, with their knobbed extremities floating in the wave.

This is one of the Polype tribe, named Stauridia producta, and as its form and structure are interesting, we will devote a few moments to its examination. We can easily sever one or two of the freely floating threads, and transfer the amputated portions to one of the live boxes of the microscope. The motions and appearance of the club with its organs will be, for a while, little affected by the violence.

The long cylindrical thread is inclosed in a transparent horny tube, which, however, so closely invests it, that it is with difficulty distinguished. The club-shaped head, or individual polype, is an enlargement of the thread, which protrudes from the investing tube. It is swollen in the middle and rounded at the end ; and many of the heads, which are more ventricose than the rest, contain a bubble of air in the centre. This air is doubtless taken-in at the mouth, which is situated at the extremity ; for, though you can discern no perforation, yet there is an aperture capable of being opened widely at the pleasure of the animal, and surrounded by protrusile, contractile, and expansile fleshy lips. I have several times seen this mouth opened, and partly turned outwards, in kindred species ; and once I had an opportunity of witnessing a quite unexpected use to which it was applied, viz., that of a great sucking disk. I had put the animal into such a live-box as this ; the two glass surfaces being just sufficiently wide apart to allow it free liberty to turn about in all directions as far as it wished. On my looking at it after a momentary interval, I saw that the extremity had suddenly become a large circular disk of thrice the diameter of the body : its substance was gelatinous, full of granules, arranged concentrically. I neither saw this disk evolved nor retracted ; but after some time, on looking at it, the same phenomenon was repeated. In order to obtain a better sight of it, but without suspicion of what I was about to effect, I slightly turned the tube of the box, carrying with it the sea-weed to which the polype was attached, my eye upon it attentively observing all the time. The base of the polype moved away from its position, but the broad disk was immovable. I continued to turn the upper glass, until at length the body was dragged out so as to be considerably attenuated ; still the disk maintained its hold on the lower glass, with no other change than that of being elongated in the direction in which it was dragged. At length it slowly gave way, and resumed its original shape by gradual and almost imperceptible diminution of the circumference.

Around this expansile, but now fast closed mouth, you observe four tentacles, radiating in a plane at right angles to the axis of the thread, towards the four cardinal points; they are long, slender, straight, and each is terminated by a globose head of considerable size, resembling the arms of certain screw-presses, which are loaded with terminal globes of metal to increase their impetus when turned.

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

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