But this huge proboscis disappears as rapidly and as wonderfully as it was revealed. Commencing at what is now the outer extremity, which is quickly tumed-in, the whole swiftly returns to its cavity in the inverse order to that in which it was extruded; and now that it is all engulfed, we marvel that so vast a sac can be packed away in so slender a case.

In this instance the armour of the proboscis is feeble; but we have species which are very elaborately armed. There is a minute species of Lombrinereis, which commonly appears in our aquaria after they have been some time established, and breeds in vast numbers on the fioccose matter that clogs the bottom and sides. In this tiny Worm there is a formidable array of jaws, resembling black hooks, which we may discern through their pellucid tissues, snapping and cutting viciously like so many pairs of hooked scissors. Though I have often had this little species in my tanks in copious abundance, I regret to say I cannot find any at this moment for our examination,, and shall therefore content myself with translating for you MM. Audouin and Milne-Edwards' description of the jaws, as they appear in a closely-allied form, but of far greater dimensions, Eunice.

" The proboscis is not very protrusile; when it is withdrawn its external orifice is longitudinal, and the jaws are fixed on each side, all facing the medial line. When it is projected, however, the two margins of the longitudinal cleft become transverse in separating, and the jaws follow the same movement, and diverge in the ratio of their forwardness. A kind of lower lip which is affixed to the under side of the proboscis is composed of two horny blades united towards their front extremity, and prolonged behind into points. The jaws are to the number of seven ; three on the right and four on the left ; the two upper ones are perfectly alike, and mutually opposed; they are large, narrow, pointed, re-curved hook-wise at the tip, and jointed at their hinder ends on a double horny stem shorter than themselves. The second pair of jaws are large, broad and flat, mutually alike, and jointed on the lower side of the first pair; . . . their internal edge is straight and cut into deep teeth. The third pair are small, thin, concave, and notched ; they are affixed by their inferior edge outside and in front of the second pair, which they conceal during repose. Finally, the supernumerary jaw, which is found on the left side only, is small, semicircular, toothed, and placed between the second and third pairs. All these pieces are surpassed by the margin of the proboscis, which is often hard and black."*

From this complex and formidable mouth we will pass to one of quite another form, not less effective, perhaps more formidable, but ordained by the goodness of God to be a most valuable agent in the relief of human suffering. I mean the medicinal Leech, of which we can readily procure a specimen from our friend the apothecary.

Here it is. There is no protrusile proboscis, but the throat is spacious, and capable of being everted to a slight degree. The front border of the mouth is enlarged so as to form a sort of upper lip, and this combines with the wrinkled muscular margin of the lower and lateral portions to form the sucker. With the dissecting scissors I slit down the ventral margin of the sucker, exposing the whole throat. Then the edges being folded back, we see implanted in the walls on the dorsal region of the cavity three white eminences of a cartilaginous texture, which rise to a sharp crescentshaped edge ; they form a triangular, or rather a triradiate figure.

Now, if you recollect, this is the figure of the cut made in the flesh wherever a Leech has sucked, as it is of the scar which remains after THROAT OF LEECH LAID OPEV. the wound has healed. For these three little eminences are the implements with which the animal, impelled by its blood-sucking instincts, effects its purpose. But to understand the action more perfectly, we must use higher powers. * " Litt. de la France," ii. 138.

I dissect out of the flesh, then, one of the white points, say the middle one, and laying it in water in the compressorium, flatten the drop, but use no more pressure than just enough for that. Now I apply a power of 150 diameters, and we will look at it in succession. You have under your eye a somewhat pellucid mass, of an irregular oval figure, and of fibrous texture, one side of which is thinned away apparently to a keen edge of a somewhat semicircular outline. But along this edge, and, as it were, imbedded into it for about one-third of their length, are set between seventy and eighty crystalline points, of highly refractive substance, resembling glass. These points gradually decrease in size towards one end of the series, and at length cease, leaving a portion of the cutting edge toothless. At the end where they are largest they are nearly close together, but at length are separated by spaces equal to their own thickness. The manner in which they are inserted closely resembles, in this aspect, the insertion of the teeth in the jaw of a dolphin or crocodile.

But this appearance is deceptive. By affixing the little jaw to the revolving needle, we bring the edge to face our eye. It is not an edge at all ; but a narrow parallel-sided margin of considerable breadth. And the teeth are not conical points, as they seemed when we viewed them sidewise, but flat triangular plates, with a deep notch in t^ieir l°wer ec^oe - Tnus tney partly embrace, and are partly inserted in, the margin of the jaw. Observe now how beautifully this apparatus subserves the purpose for which it is

JAW OF LEECH (in part). intended. By means of its sucker, the Leech creates a vacuum upon a certain part of the skin, exactly like that

produced by a cupping-glass. The skin covered is drawn into the hollow so far as to render it quite tight, by the pressure of the surrounding air. Thus it is brought into contact with the edges of the three jaws, to which, by means of powerful muscles attached to them, a see-saw motion is communicated, which causes the little teeth soon to cut through the skin and superficial vessels, from which the blood begins to flow. The issue of the vital fluid is then promoted by the pressure around, and so goes on until the enormous stomach of the Leech is distended to repletion.

It has been suggested that this whole contrivance, with the instinct by which it is accompanied, is intended for the benefit of Man, and not of the Leech. Blood seems to be by no means the natural food of the Leech; it has been ascertained to remain in the stomach for a whole twelvemonth without being digested, yet remaining fluid and sound during the entire period : while, ordinarily, such a substance cannot in one instance out of a thousand be swallowed by the animal in a state of nature. Whether this is so or not,—whether man's relief under suffering was the sole object designed, or not, it was certainly one object ; and we may well be thankful to the mercy of God, who has ordained comfort through so strange an instrumentality.

The progress of marine natural history, as studied in the aquarium, has made our drawing-rooms and halls familiarwith a multitude of curious and beautiful creatures which a few years ago were known only, and that very imperfectly, to the learned professors of technical science. Among the forms which embellish our tanks are several species of Serpula, and Worms allied to it. The shelly contorted tube which this painted Sea-worm inhabits, and which it has built up around its own body, with stone and cement which that body supplied, is well known to you ; as is also the curious conical stopper with which it closes up its bottle as with a cork, when safe at home, and the lovely crown of gorgeously coloured fans which it expands when it takes ("the air" T was about to say, but rather) the water. You are familiar, too, with the lightning-like rapidity with which, while in health and vigour, the Serpula, on the slightest alarm, retreats into his fortress, taking care to clap-to the door after him. But perhaps you have never had an opportunity of examining the mechanism by which this rapid flight is effected.

As there are two distinct movements performed by the Worm,—the slow and cautious and gradual protrusion, and the sudden and swift retreat,—so there are two distinct sets of organs by which they are performed. Shall I sacrifice one from this fine group to demonstrate the mechanism % Well, then, I carefully break the shelly tube, and extract the worm uninjured.

Its form is, you perceive, much shorter and more dumpy than you would have supposed from looking at the tube ; and it is somewhat flattened, having a backand a belly-side. On the former there is a sort of shield, the sides of which bear wart-like feet,—about seven pairs in all,—which are perforated for the working of protrusile pencils of bristles, similar in structure and in function to those which we lately examined.

Here is one of the pencils extracted. To the naked eye it is a yellowish body with a satiny lustre ; and this effect depends upon the light being reflected from a number of nearly parallel lines,—the staves of the spearlike bristles,-—which the eye cannot resolve in detail. A drop of the caustic solution of potash cleanses the bundle from the fleshy matter which would otherwise obscure the vision, and now I place it on the stage.

With this power of 400 diameters you see a multitude —some twenty or thirty, or more—of very long, slender, straight rods, of a clear yellowish horny substance, set side by side, like a sheaf of spears in an armoury. Each one merges, at its upper end, into a sort of blade, which is slightly bent, and which tapers to an exceedingly fine point. But its chief peculiarity is that the blade has a double edge, not like a two-edged sword, the edges set on opposite faces, but on the same face, set side by side, with a groove between them; and each head is cut with the most delicate and close-set teeth, the lines of which pass back upon the blade, as in our sickles.

PUSHING POLES OF SEBPULA.

These pencils of spear-like bristles are the organs by which the protrusion of the animal is performed. Their action is manifestly that of pushing against the walls of the interior, which on close examination are seen to be lined with a delicate membrane, exuded from the animal's skin. The opposite feet of one segment protrude the pencils of bristles, one on each side, the acute points and teeth of which penetrate and catch in the lining membrane; the segments behind this are now drawn up close, and extend their bristles; these catch in like manner ; then an elongating movement takes place ; the pencils of the anterior segments being now retraced, they yield to the movement and are pushed forward, while the others are held firm by the resistance of their holding bristles ; thus gradually the foreparts of the animal are exposed.

But this gradual process would ill suit the necessity of a creature so sensitive to alarm, when it wishes to retreat. We have already seen how, with the fleetness of a thought, its beautiful crown of scarlet plumes disappears within its T

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