Part 4

At the very first glance into this little rock-hollow, all fringed with crimson and purple weed, lined with scales of lilac coralline, and partly shadowed by the olive fronds of the leathery tangle, we discern many forms of animal life. Here, for instance, is a fine handsome shelled mollusk, the Purple-spotted Top. Before we take him up, let us notice for a moment with what an easy even movement he glides along over the leaves of the sea-weed, now over the stony projections of the pool, now on the broad weeds again. On lifting the shell, we find that the fine, fleshy, apricot-coloured animal clings with considerable force to the weed; and on transferring it to a glass bottle, we get a better sight of the organ by which it maintains both its stability and its movements. The under-surface of the creature, then, forms a long, nearly parallel-sided sole, abruptly pointed behind, where it stretches to a considerable distance in the rear of the shell, and bounded in front by a slightly-thickened transverse rim, a little arched, and projecting on each side. This organ is the foot, and it is composed of muscular fibres elaborately interwoven, much as in the human tongue, whereby great versatility and power of motion are communicated to it; indeed, when in motion, it strongly reminds one of the human tongue.

PLATE 1.

P. H. GOSSE, del. LEIGHTON, BROS.

DOG-WHELK. PELICAN’S FOOT. TOP. COWRY. ]

The sensitive and muscular foot of our captive has already taken hold of the glass side of its prison, and it is now smoothly mounting up it. With a lens you may see that though it is one undivided area, yet in the arrangement of its muscles, it is separated into two portions by a line which runs down the middle; and that these two sides move alternately. The muscles of the right half, for example, are moved a little onward, and take a fresh hold of the ground, while those of the left remain clinging; then the right half clings, while the left relaxes and advances a little beyond the right, and again clings, when the right makes its forward move. So that the effect is exactly that of two feet advancing by alternate steps; and if your own two feet were enclosed in one elastic stocking, your own progress would appear very much like that of the Trochus. Indeed, some shell-fishes not distantly allied to this, as the pretty little Pheasant-shell, which I occasionally find among these rocks, really have the foot divided into two distinct and separate halves, in which this alternate motion is, of course, more obvious.

Looked at from above, we discern that this foot thickens towards the middle, where it is overlapped by a broad wing-like expansion on each side. This, for manifest reasons, is known by the name of the cloak or mantle. In all cases it performs important offices in the economy of the animal, as I shall presently describe; and in this instance we see it is adorned along its edges with certain lappets and long fleshy taper threads (called cirri), which wave vivaciously to and fro as the creature crawls. These are probably the seats of a delicate sense; perhaps receiving impressions analogous to those of touch, from the strokes they continually make on the surrounding fluid.

In front we see a distinct head, with a broad flat muzzle not altogether unlike that of an ox. On each side of the back part of this head, there is another long taper thread: these are called tentacles, but neither in form nor in structure can we discern any difference between these and the cirri that fringe the mantle. In all probability they are alike organs of a highly delicate sense of touch.

THE TOP’S EYES.

Immediately behind each of these head-tentacles you see a little wart, which has a black bead set as it were in its substance. You have often, doubtless, observed the similar black points that are placed at the tips of the upper pair of the horns (tentacles) of the common garden snail; and I daresay, when a child, you have amused yourself by touching them, and noticing how instantaneously the sensitive creature would roll them in, so to speak, concealing them far in the interior of the inturned horns. And every child is taught that these black spots are the snail’s eyes; and so, indeed, they are; and these spots on our Top’s warts are its eyes too, notwithstanding that some learned naturalists, apparently from the mere love of paradox, have affected to doubt the fact that such is their function. If you could dissect out one of these points, and submit it to careful examination with a good microscope, you would find all the parts essential to an organ of vision; there is a sclerotic coat, a distinct little pupil and iris, a cornea in front, and a dark pigment layer within, with vitreous and aqueous humours, and even a crystalline lens for the condensation of the rays of light. Minute these parts are, to be sure, but not less exquisitely finished for that. Indeed, the more skill they require in the demonstrator, the more they reflect the inimitable skill of the Creator. Swammerdam, the Dutch physiologist, who so beautifully showed the structure of the snail’s eye, seems to have feared the doubts of his conclusions that would ensue from the difficulty of repeating his investigations. “But who will credit this?” he says; “for does it not seem impossible that on a point not larger than the nib of the pen with which I write, such exquisite art and so many miracles should be displayed?”

SPIRAL SHELLS.

Now, leaving the animal, though we might devote a few moments to the admiration of its rich colours, adorned as is its deep yellow hue with lines and clouds of deeper brown, let us look at the shell, the solid house of stone, which our friend Trochus has himself built up to cover his head in the hour of danger. How well has he combined the utile cum dulci!--the comfortable with the ornamental! Its general form is that of a cone of much regularity, but with an oblique base, and perhaps you may be surprised to learn that this conical form is but the result of the winding of a very long cone upon itself in a spire. But if you examine a dead shell with care, you will see that it is so. Supposing you had a very long and slender hollow cone of plastic material, and, beginning with the acute point, you twined the whole upon itself, descending in a spiral form, you would have the representation of a turbinate shell, which, by a little gentle pressure of the fingers, might be moulded, without at all losing its essential character, into the exact shape of our Trochus, in which the progress of the spire can without difficulty be followed as well by slight inequalities of surface as by the arrangement of the colours.

It is one of our showy shells. This specimen before us has for its ground colour a chaste, cool grey, occasionally varied with tints of reddish buff, but most conspicuously adorned with a series of large and regular spots of purplish crimson running along the lower angle of the spire from the base to the summit. Each of these spots passes off into an oblique line above, the repetition of which augments the beauty of the pattern.

The interior of the shell has a glory of quite another character. It is covered with a coat of nacre or pearl, of exceedingly brilliant and rich lustre, and the presence of this inward pearliness is quite characteristic of this genus, and of most of the others belonging to the same family, the Turbinidæ. Many of the fine large tropical species are specially conspicuous for this adornment, as I have seen in those that lie along the dazzling beach of coral-sand in lovely Jamaica. The pearl of these shells is used in the arts. De Montfort mentions a necklace which he had seen, that was made out of the nacred part of the shell of the Turbo smaragdus, and which was much more brilliant and beautiful than any of the finest orient pearls. And Chenu observes:--“Les grandes espèces fournissent une fort belle nacre, employée pour les ouvrages de marqueterie. Quelques espèces ont reçu des noms sous lesquels les marchands les distinguent: il y a le Burgau ou Nacré; la Veuve Perlée, dont les tubercles extérieurs usés ressemblent à des perles; la Bouche-d’Or, dont la nacre est d’un beau jaune doré; la Bouche-d’Argent; le Perroquet, ou Turbo Impérial,” etc.

At another time we may examine the structure of shell, and inquire by what instruments and with what materials the ingenious animal contrives to construct so strong and so elegant a dwelling. For the present, however, as the month is January, we shall, if we sit still longer, run the risk of “catching a cold,” if we catch nothing else, though the wind is in the south, and the temperature is so mild for the season.

THE DOG-WHELK.

Therefore, we will move about and pursue our researches among the rocks and under the loose stones. Well, we are rewarded with other specimens: here are several neat little shells, with a lengthened spire, and with a remarkably thickened lip. This is the little Thick-lipped Dog-whelk, a very common mollusk with us under such stones as these at low water-mark. And here is another species of the same genus, the Netted Dog-whelk, which is a much larger shell, being nearly twice as long as the former, and marked with close transverse furrows, which, crossing the longitudinal ribs at right angles, give a peculiar reticulate surface, on which the specific name is founded.

Comparing these shells with the Trochus, we see that they have a deep notch cut in the front part, of which no sign appears in the latter; and this mark, trivial as it may seem, is an important indication of the habits of the animal. The inhabitants of all shells which have this notch are carnivorous, while those with simple lips are herbivorous. The Trochus gnaws or rather rasps away the tender growth of marine vegetation, or the fronds of the grown Algæ, with its remarkable palate-ribbon, all studded with reversed points, of which I may find another opportunity to speak. The Dog-whelk, on the other hand, acts the part of a cannibal ogre, feeding on his simpler brethren of the bivalve shells; storming their stony castles, in which they seem so secure, by open violence.

Look at this old valve of a Mactra. Like hundreds more that you may pick up at high water-mark, it is perforated by a tiny hole near the hinge, so smooth and so perfectly circular, that you would suppose a clever artisan had been at work drilling the massive stony shell with his steel wimble. No such thing: the Dog-whelk has done it: this is the breach which he so scientifically effected in the fortress; and hence he sucked out the soft and juicy and savoury flesh of his miserable victim.

In order to understand his plan of operations, let us put down our captive, and see him crawl. He is not long before he begins to march, on his broad oblong foot, which, as you observe, is cream-coloured, elegantly splashed and speckled with dark-brown. But before he moves he thrusts out a long cylindrical proboscis from the front of his head, which he carries high aloft and waves to and fro; and this organ, we see, fits into the deep notch in front of the shell. This proboscis is his drilling-wimble.

THE DOG-WHELK’S DRILL.

This organ is itself a study. Long as it is when extended, it can be thoroughly drawn within the body; and there it forms two fleshy cylinders, one within the other, exactly like a stocking half turned on itself. There are proper muscles attached to its walls, and to the interior of the head, by extremities which are branched in a fan-shape, so as greatly to strengthen their insertions; and these, by contraction, draw the one portion within the other. Then there is a broad hoop of muscle, which, passing round the inner cylinder, by contracting pushes it out, and lengthens it. Within the interior of this latter there is a long narrow ribbon of cartilage, which is armed with rows of sharp flinty points, turned backwards; and this tongue or palate, as it is variously called, is the Dog-whelk’s weapon.

We cannot induce the Whelk to attack his prey just when we please; but he has been detected in the operation, and I will describe it. With his broad muscular foot he secures a good hold of the bivalve, and having selected his point of attack, in general near the hinge--a selection which probably looks more at the superiority of the meat within than at any peculiar facility in the perforation--he brings the tip of his extended proboscis to the point, so that the silicious teeth can act on the shell. Hard as is the calcareous shell, it is not proof against the flint; for, without any solvent excretion, the aid of which some physiologists have been ready to suppose, these glassy points, grating round and round as on a pivot, soon wear away the substance, and gradually bore the tiny aperture which exposes the sapid morsel.

Continuing our researches, we find, deep in a rocky pool under a tuft of weed, a shell of a peculiar form, because of the enormous expansion of its outer lip. It is known as the Pelican’s-foot, from the resemblance which this lip with its diverging ribs bears to the webbed toes of a water-fowl. This, too, is a carnivorous species; and though it is somewhat rare to detect the animal moving, even though kept alive in captivity, yet by carefully examining this one in its deep pool, before we disturb its equanimity, we can just see the proboscis protruding from the wide square notch in the shell, and discern that it is rather prettily coloured, being marked with spots of opaque white on a rose-coloured ground.

This species is interesting from the changes of figure which it undergoes in its progress from youth to maturity. While young the shell is simple, with no trace of the expanded lip; and it is only at mature age, and rather suddenly, that the shell makes its remarkable growth into these far-projecting points and angles, the augmented thickness of which is, moreover, at least equally conspicuous with the expanse.

THE COWRY.

But far more remarkable changes take place in the growth of the shell in a family of signal beauty, of which I discern a specimen in yonder cavernous hollow. The family I speak of is that of the Cowries; and this individual represents the only species that is indigenous to our seas--the little Furrowed Cowry. Let us pause awhile to admire it, for it is one of the very loveliest of our marine animals.

The shell itself is doubtless familiar to most of my readers, for it is to be picked up on every sandy beach. It varies in size from that of a split pea to that of a large horsebean. It is elegantly marked all over with transverse ridges. These ridges are porcellaneous white, and the alternate furrows between are purplish, or flesh-coloured. The larger specimens commonly display three spots of dark brown, arranged lengthwise. But probably few are aware how very elegant a creature it is when tenanted by its living inhabitant, and crawling at ease in clear water. The foot, on which it glides with a slow but smooth motion over the surface of the rock on which it habitually dwells, or, if you please, on the bottom of the saucer of sea-water in which you are examining it, is a broad expansion spreading out to twice the superficies of the base of the shell. Above this is the fleshy mantle, which is so turned up as closely to invest the shell, conforming to its shape, and even fitting into the grooves between the ridges. This mantle can be protruded, at the will of the animal, so far that the two sides meet along the top of the shell, and completely cover it, or it can be completely retracted within the wrinkled lips beneath; and it is capable of all gradations of extension between these limits. From the front of the shell protrudes the head, armed with two straight and lengthened tentacles, answering in function and appearance to the upper pair of horns in a snail; except that the little black points which constitute the visual organs are not in this case placed at the tips, but on a little prominence on the outside of the base of each tentacle. Above and between these, which diverge at a considerable angle, projects the proboscis, a rather thick fleshy tube, formed by a flat lamina, with its edges bent round so as to meet along the under side. The interior of this proboscis is lined with delicate cilia, by whose constant vibrations a current of water is drawn into the tube and poured over the surface of the gills, for the purpose of respiration. This current may be readily perceived by any one who will take the trouble to watch, with a pocket-lens, a Cowry crawling along the side of a phial filled with sea-water. By placing the vessel between your eye and the light, and fixing your attention on the front of the proboscis, you will presently perceive the minute particles of floating matter (always held in suspension, even in clear water) drawn in various directions towards the tube, with a motion which increases in velocity as they approach, and at length rapidly sucked in, and disappearing one after another within. It is an interesting sight to see, and one that cannot be looked on without delight and admiration at this beautiful contrivance of Divine Wisdom, for the incessant breathing of the respiratory organs in water charged with vivifying oxygen.

Let us look at the vivid hues of all these organs. The foot, which expands to so great a length and breadth behind the shell, is of a buff or pale orange ground-colour, delicately striated with longitudinal undulating veins of yellowish white. The mantle which embraces the shell is of a pellucid olive, thickly mottled and spotted with black, and studded with glands protruded through its substance, of light yellow; and is often edged with a narrow border of red. The proboscis is vermilion-red, varying in brilliancy in different individuals. The tentacles are of a paler tint of the same colour, speckled with yellow.