See "Edin. New Philosophical Journal," for April, 1857.

stolon, after leaving the point of its origin, increases rapidly in diameter, and sends out irregular branches. The tips of these branches are covered with a glutinous cement, by which they attach themselves tenaciously to glass, or other surface near them. Having attached themselves, they expand laterally, at the same time throwing out finger-like prolongations, which, as they come in contact with each other, coalesce, until a fleshy plate is found adherent to the glass. Polypes are developed both from the loose branches and the attached polypary; and the latter is clearly seen to be permeated by a beautiful system of anastomosing canals, connected with the hollow bodies of the polypes. Within these canals may be detected an intermittent flow of fluid, containing particles, the dancing motion of which indicates the presence of ciliary action ; and which, having passed in one direction for a short time, are arrested, and, after a slight period of oscillation, begin to flow in an opposite direction."

The polypes which are developed from this living carpet are not all of the same form. ISTo fewer than five distinct sorts exist, at one and the same time ; and I doubt not we shall be able to find and to identify them all, on this well-grown specimen.

First, there are the alimentary polypes, which we have already cursorily glanced at. Within the space inclosed by the two circles of tentacles, there is a mouth with soft protrusile lips, which can be pushed out and folded back, so as to hide tentacles, column, and all.

Scattered among these we see numerous polypes, which agree in general form with these, but with some remarkable subtractions and additions. They have no mouth nor stomach, and the tentacles are reduced to the smallest possible warts or protuberances like small teeth on the dilated tip. But the additions are still more peculiar. From the middle part of the column a number, from four to nine, of great oval sacs project, each attached hy one end, while the other stretches out horizontally, thus surrounding the slender column. Each of these sacs is an ovarian capsule, and contains several ova of a brilliant yellow or crimson hue. Thus we have the second form, that of the reproductive polypes.

In some places single ovarian capsules stand up alone from the fleshy carpet, agreeing in every respect with those which we have just examined, except that they are sessile, instead of being carried by a polype.

The fourth form is that of the tentacular polype. Here and there, from amidst the forest of shorter polypes, both alimentary and reproductive, white threads are seen protruding, which extend to a length four or five times as great as theirs, and hang down or loosely float in the water. They are found on the outskirts of the whole compound structure, and at each extremity of the long diameter of the mouth of the supporting shell ; so that they must, in their natural condition, reach to the ground, along which the crab-tenanted shell is carried, enabling the Zoophyte to seize and appropriate the atoms scattered by the crab whenever he takes his meals. The tips of these organs are covered with a dense pavement of large thread-cells; and they must doubtless perform the office of general purveyors to the composite animal.

But still more remarkable, more extraordinary than all we have been considering, are the objects which are now in view in the field of the microscope. You see a number of bodies, which Dr. Wright calls ophidian or spiral polypes ; and which, as he truly observes, are " like small white snakes, closely coiled in one, two, or three spirals, and grouped immediately round the mouth of the shell." The habits of these polypes are still stranger than their forms. " When touched they only draw their folds more closely together. But if any part of the polypary, however distant from them, be irritated, the spiral polypes uncoil, extend and lash themselves violently backwards and forwards, and then quickly roll themselves up again ; and that not irregularly or independently of each other, but all together, and in the same direction, as if moved by a single spring. A violent laceration of the polypary causes these polypes to remain extended and stretched like a waving and tremulous fringe across the mouth of the shell, for several minutes. The ophidian polypes (evidently a barren modification of the reproductive polype) are never found in any other situation on the polypary than in that before described, or round the margins of accidental holes in the shell. They have no mouth and the tentacles are rudimentary. The walls of the body are very transparent, from the extreme vacuolation of the inner tissue. The muscular coat, as might be expected, from the active movements of the polypes, is highly developed, and forms a beautiful object on the dark polarised field of the microscope, each spiral coil shining out as a bright double ring divided by four dark sectors. The outer tissue of the whole body and tentacles is crowded with the larger thread-cells. The ophidian polypes are, doubtless, organs of defence or offence, like the motile spines and bird's head processes of the Polyzoa, or the pedicellarise of the Echinodermata ; but it is difficult to assign a reason for their peculiar situation. They vary much in number and size, in different specimens of Hydractinia, but are rarely altogether absent."*

The reflections of the able zoologist who first called attention to these varied developments, and his comparisons of them with those of another polype-form which we have lately been observing, are so interesting and instructive that you will not deem it needful that I should apologise for citing them. " In our consideration of the Hydractinia" he observes, " our attention is arrested by the multitude of objects grouped together to constitute a single animal, their variety in form, and the sympathy * Dr. Wright, op. cit.

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.

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