Beyond this point I have not pursued the history of the little Turris from personal observation; nor am I aware that any naturalist besides has studied the development of this particular genus. But the history of other genera is known; and as the phenomena they exhibit are quite parallel to those which I have been describing, so far as these have been traced, we may fairly conclude that there is the same parallelism in the subsequent stages.

Assuming this, then, the little crimson stem with four rays,—a veritable polype,—buds four more tentacles in the interspaces, making the total number eight; these in like manner increase progressively to sixteen, thirty-two, and sixty-four. It now possesses a close resemblance to the Hydra of our ditches, only having more tentacles; &nd, like it, the Medusa-larva buds forth from its sides young Hydra-like polypes, which take the form of their immediate parent, fall off, attach themselves, bud forth more, and so on. All these catch living prey with their tentacles, swallow them with their mouths, and digest them with their stomachs, exactly like real polypes, and thus produce generation after generation of similar beings.

Years may pass in this stage, during which numberless polypes are formed. At length the original stock, or any one of its descendants, takes-on an important change. Its body lengthens, and becomes cut as it were into a number of rings, as if tied tightly round with thread, or like the body of an Annelid. These segments become increasingly distinct, until at length each is seen y 2 to be a shallow cup, notched at its margin, and sitting in the concavity of the one next below it. This structure is developed first in those at the free extremity of the polype, and progressively downward; and the terminal cups are nearly free, rocking in their successors with every wave, while the lowest segments are scarcely visible as such.

At length the extreme cup rocks and oscillates until the slender thread of connexion is snapped, and it is free. It at once turns itself over, so as to present its concavity

TURBIS AND ITS YOUNG.

downwards, and, contracting its margin with the wellknown pulmonic spasm, shoots away with the movement as well as the form of a veritable Medusa. The little progeny has at length, after passing through so many changes, returned to the image of its parent.

Such are, in brief, the phenomena of one of the most remarkable series of facts that modern zoology has discovered, and which have been propounded under the title of the Law of Alternation of Generations.* See pages 333, 334, infra.

Chapter XVIII. Zoophytes

It is pleasant to go clown to the shore on a bright autumnal morning at low water, when the tide has receded far, exposing great areas of wet sand, and wildernesses of rugged rocks draped with black and red weed. It is pleasant to make our way on cautious foot round some frowning point whose base is usually beaten by the billows; to travel among the slippery boulders, now leaping from one to another, now winding between them, now creeping under their beetling roofs; to penetrate Avhere we have never ventured before, and to explore with a feeling of undefined awe the wild solitudes where the hollow sea growls, and the grey gull wails. It is pleasant to get under the shadow of the tall cliffs of limestone, to creep into low, arching caves, and there to stoop and peer into the dark pools, which lie filled to the brim with water as clear as crystal, and as unruffled as a well. What little worlds are these rugged basins! How full of life all unsuspected by the rude stone-cutter that daily trudges by them to and from his work in the marble quarry of the cliff above ! What arts, and wiles, and stratagems are being practised there ! what struggles for mastery, for food, for life ! what pursuits and flights ! what pleasant gambols! what conjugal and parental affections ! what varied enjoyments ! what births ! what deaths ! are every hour going on in these unruffled wells, beneath the brown shadow of the umbrageous oar-weed, •or over the waving slopes of the bright green Ulva, or among the feathery branches of the crimson Ceramiiamf I have just been exploring some of these rock-wells, and have rifled them of not a few of their living treasures, bringing home the spoils, that you may share with me in the enjoyment of examining them.

The Zoophytes* are here in their glory. Such places as those I speak of are the very capitals of the zoophytic nation. Look at this great leaf of the fingered Tangle : see how its broad olive-brown expanse is covered with tiny forests of white branching threads, which spread and spread till they run off into the fingers of the much split leaf; and not only on one side, for the under surface is as densely clad with the shaggy burden as the upper; the smooth leathery tissue being covered with a network of creeping roots, branching and radiating everywhere, like the railways on Bradshaw's map.

This double forest is wholly composed of a single species, called Laomedea geniculata ; nay, I believe it is but one single individual. That is to say, the whole of these multitudinous ramified threads and stems, with their innumerable polypes,! have all extended by gradual though rapid growth from a single germ ; and all are connected even now, so that a common life pervades the whole. But we will look awhile at it in detail, till we have mastered its external features, and then I will tell you something of its history and economy.

With the unassisted eye we can discern plainly enough the outline and plan of this compound organism. Along the smooth and slippery surface of the olive weed runs a

From the Greek £u)oi'(zoon), an animal, and tpvrbv (phuton), aplant. A term applied to a large class of animals bearing 'polypes, and whose entire skeleton, called a polypar-y or polypidom, more or less resembles a plant or tree in its appearance and growth.

The term Cozlenterata is now substituted for this in systematic natural history. See Prof. Greene's excellent " Manual of the Anim. Kingd." ii. Lond. 1861.

t From the Greek 7to\vq (polus), many, and ttovq (pous), afoot. A low order of animals having numerous tentacles or feelers round the mouth, and often bearing a strong resemblance to flowers.

fine thread of pellucid white appearance, so firmly adherent that if you attempt to remove it with a needle's point, you find that you only tear either the leaf or the thread. The course is generally in a straight line, but does not ordinarily pursue the same direction far, commonly turning off with an abrupt angle at intervals of about an inch; and thus meandering in a zig-zag fashion, very irregularly, branching frequently, and uniting with a thread already formed, when the creeping one has to cross it.

Thus the basal network is formed; but, meanwhile, from every angle, and often from intermediate points, a free erect thread has shot up, like the stem of a tiny plant, to the height of an inch, rarely more ; not, however, straight, but with frequent zig-zag angles, whence the name geniculata, or " kneed." At every angle a slender branch is sent forth, pursuing the same direction as that of the joint from the summit of which it issued, and terminating in a tiny knob. In the angles of some of these branchlets are seated oblong vesicles, twice or thrice as large as the terminal knobs. And this is pretty well all that we can make out with the naked eye.

Cutting carefully off with scissors a narrow strip of the leaf, I drop it into the parallel-sided cell of glass half-filled with sea-water, and examine it first with a low power and afterwards with a higher. We now see that the creeping thread is a tube of horny substance, flattened on its under side, and that the erect stems and their branches are similar tubes, whose cavities are in free communication with that of the creeping root. The wall is thin, and perfectly transparent and colourless ; the whiteness of the whole being dependent on a soft medullary core of living jelly, which permeates the whole structure, on which the horny sheath is, as it were, moulded.

This medulla is pierced with a canal, through which a fluid circulates, carrying along numerous minute granules with a quivering, jerking motion; this is doubtless the nutrient fluid conveying the products of digestion to every part of the common structure.

Where the branches issue from the angles of the stem, the medulla, and consequently the horny sheath, is dilated into a knob; immediately above this there is a joint-like constriction in the tube, and the branch itself is insected by four or five such constrictions, so as to form as many rings. Its extremity then expands into an elegant cup or vase, of extreme tenuity and transparency, shaped like a wineglass, with the rim undivided, but so thin and subtle as to be seen with the greatest difficulty. These cups, or cells, are LAOilEDEA. each the proper habitation of a polype, which is nothing else but the termination (in this direction) of the living, growing, vascular pith. The latter becomes exceedingly attenuated, in order to pass through a very narrow orifice in the centre of a horny diaphragm, or sort of false bottom, which passes across the lower part of each cell. It then dilates into a soft, contractile animal, whose body—but look for yourself; for here, full in the field of the microscope, is one expanding in the highest vigour and beauty.

It is a long trumpet-shaped body of granular flesh, the mouth of which just reaches the brim of the cup, over which it spreads on all sides. From its margin spring some eighteen or twenty tentacles—the exact number

varying in different individuals—arranged in one or two close-set circles, like a crown. These organs, which, as you see, fall into elegant double curves, like the branches of a chandelier, are roughened with knobbed rings, something like the horns of a goat; this structure we will presently submit to more close examination.

In the midst of the space surrounded by the tentacular crown there is protruded, at the pleasure of the animal, a large, fleshy, funnel-shaped mouth, the lips of which are highly sensitive, continually changing their form; protruding, contracting, bending in upon themselves, now closing, now opening the mouth, and, as it were, testing the immediate vicinity, like a very delicate organ of some unknown sense.

The whole polype is much too minute for us to attempt, with any probability of success, the amputation of one of the tentacles with scissors. But by cutting off a polype, cell and all, and putting it into the compressorium, we may be able, by means of the graduated pressure, to flatten the whole, and thus discern the gnarled structure of the tentacles. A very high magnifying power is needed for this.

Here, then, we have one of the tentacles flattened between the glass plates,but still retainingits integrity. We find that the thickenings are similar in character to those of the tentacles of Sarsia,which we lately observed. They are, in fact, accu- TENTACLE OF LA01IEDEA ; flattened. mulations of cnidce, those peculiar weapons of power, which T shall presently describe in full; but here they are symmetrically arranged in single rows, each pointing upward and outward.

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