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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,[2] 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.

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?”

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.[3] 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