The four radiating vessels here carry, just before they merge into the marginal canal, a dilatation of the common flesh, which, as you see, bulges out the surface of the umbrella. We will examine one of these dilatations with the microscope.

It is, as you perceive, occupied by a number of clear globes, each of which has another minute globose body in its interior. They are very diverse in size, some beingvery small, others comparatively large ; and it is to the dimensions of these latter that the swelling of the surface of the umbrella is due. These vesicles are the eggs of the animal considerably advanced towards maturity ; and the dilatations around the radiating vessels are the ovaries.

The margin, however, presents us with the most obvious, and perhaps the most interesting, points of diversity from the Sarsia. In the little beauty before us, whose scientific name, by the way, Thaumantias you,—the pilosella, I have not yet told outline is fringed with about fifty short and slender tentacles, each of which springs from a fleshy bulb, in which is set a speck of deep purple. These collections of coloured granules, which I have already explained to be rudimentary THAUMAXTIAS. eyes, have a very charming effect ; and give a beautiful appearance to the little creature, as if its translucent crystalline head were encircled with a coronet of gems.

You shall see them, however, under circumstances which will make them appear more lustrously gem-like still. Come with me, and I will carry the glass containing our little Thaumantias into the next room. You need not bring the candle, or what I am going to show you will be quite invisible.

Take hold of this pencil, and, having felt for the glass, disturb the water with it. Ha ! what a circle of tiny lamps flash out ! You struck the body of the Thaumantias with the pencil ; and instantly, under the stimulus of alarm, every purple eye became a phosphoric flame. Touch it again ; again the crown of light flashes out, but less brilliantly; and each tiny lamp, after sparkling tremulously for a moment, wanes, and the whole gradually, but quickly, go out, and all is dark again.

But it is tired of lighting up for nothing; or its gas is exhausted; or it is become used to the pencil and is not alarmed; or,—at all events you may knock it, and push it, but it refuses to shine any more. Back with it then to the microscope, and let us see if it possesses any other points of interest for us there.

Yes : we have not exhausted the organs of the margin yet. Between the tentacles which spring from bulbs

there are a good many more, far more minute, without any bulbs;—from four to seven between every two of the primary ones. We won't mind these, but, bringing the margin itself into focus, and moving it along the stage horizontally, we presently see one and another singular organs. They are eight in all, two being placed, but irregularly, in each of the four quadrants of the circle formed by the radiating canals.

These are organs of hearing, very closely similar to those which we see imbedded in the bosom of the Snail and other Mollusca. Here they are comparatively large, and unusually well furnished. Each is a semi-oval enlargement of the flesh of the margin, in close connexion with the walls of the marginal canal, hollowed so as to inclose a capacious cavity, in which are placed a considerable number,—from thirty to fifty in this individual—of otolithes, or spheres of solid, transparent, highly-refractive

OTOLITHES OF THAUMATTTIAS.

substance. They are arranged in a double line, forming a crescent, and those which are nearest the centre are larger than those towards the extremities of the line. I believe some observers have seen oscillatory and rotatory movements among these spherules, as in the Mollusca; but I have invariably found them motionless in all the species of Medusa that I have examined, as you see them here.

One more little beauty from our stock, and we have

done with these. There is one that moves among the rest like a bead of coral, the smallest of all, yet the most brilliant. Here is another, and here another of the same sort; which has been named by Professor Edward Forbes, Turris neglecta, because naturalists before him had neglected to notice it, just as we have been doing, engrossed by its larger brethren.

Beautiful as is this little gem ; it is not so large as a dried pea, scarcely larger than a grain of hemp-seed. It is described as " mitre-shaped ;" in other words, it is a tall bell, with the margin slightly bent inwards, and the sides a little constricted. The umbrella is thick, and, beingvery muscular, is not so translucent as those we have been examining; hence it has a pellucid white appearance. But through this shines its chief beauty; the peduncle is very large, and globose at the upper or basal part, which is usually, as here, of a pale scarlet or rich orange hue.

Imbedded in this orange-coloured flesh are seen many points of a lovely rose-purple; which two colours blending together, and softened by their transmission through the sub-pellucid umbrella, have a peculiar brilliancy. But stay ! here I have one more advanced in age, which will exhibit some peculiarities of interest in the economy of these frail but charming creatures.

In this specimen, which is somewhat larger than the former, the margin of the umbrella is a little turned back, displaying more clearly the peduncle with its brilliant ovaries. These, too, are more turgid, and the rosy points are seen projecting from their interior, and some of them even ready to fall. And look ! here on the bottom of the glass are lying half-a-dozen or more of similar purple points, whose rich hue renders them plainly discernible, after a slight searching, to the unassisted eye I will collect one or two with a tube of glass, and submit them to your examination under the microscope. Y You now discern that these bodies are perfectly oval in form. One might, indeed, call them eggs,—for they perform the part of such organisms,—but that they have soft walls, covered on their whole external surface with fine vibratile cilia, by the action of which they are endowed with the power of free locomotion. We see them, in fact, gliding about the water of the live-box under view, with an even and somewhat rapid motion, which appears to be guided by a veritable will. Under this power they are seen to be of a soft rich lakecrimson hue, all over.

These little gemmules have a somewhat romantic history of their own. I am afraid that these we see are too recent to afford us any help in tracing it, and therefore I must be satisfied with telling you what I have observed of it on former occasions.

After the beautiful little Coral Jelly has swum about a few days, the umbrella begins to turn outward and backward, and to contract more and more, until at length it lies in shrivelled folds around the top, leaving the whole peduncle exposed. Long before this, the creature has lost its power of swimming, and lies helpless on its side upon the bottom. Meanwhile the orange ovaries have swollen; the purple gemmules have become developed, and have gradually worked their way through the ovaries, and fallen one by one upon the bottom. There then they glide about for a little time, perhaps for a day or so, by means of their vibrating cilia.

At length each little gemmule loses its power of wandering, its motion becomes feebler and more intermitted, and finally ceases altogether. The little being now rests on some solid body,—a stone or a shell,—to which it firmly adheres. Its two extremities grow out, adhering as they extend, and sometimes branching, but still in close and entire contact with the support. At length, after a day or two, from some point of the upper surface of this creeping root, a kind of wart buds forth, and soon grows into an erect slender stem, which presently divides into four straight, taper, slightly divergent tentacles, which grow straight upward to a considerable length. The whole structure retains the rich purple hue of the original gemmule.

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.

Page 50 of 65