The new animal is evidently now in its final state, needing only development of its parts, which it would obtain, if in freedom, by successive moults, to acquire the adult form.

If we now submit the exuviae in detail to a power of 220 diameters, we shall obtain some interesting views of the structure. The slough of the eyes in particular presents one of the most exquisite objects that you can behold. They are somewhat pear-shaped, with the facetted portion well defined. It is the appearance of these facets, varying according as the perfectly hexagonal outline of each, or the smooth and glossy convexity, comes into focus, that is so peculiarly charming.

Heturning now to the examination of one of the living Zoeas, you perceive that the three pairs of pencilled limbs do not represent any of the true legs; for the transparency of the integuments allowing the interior to be clearly seen, and the organs of the imago being matured and just ready for sloughing, you discern, with the most beautiful distinctness, the fingered claws (short and stumpy, it is true, as compared with their perfect form in the newly-freed imago) folded down upon the breast within the skin, the second pair as large as these, and traces of others beneath them,— all these forming two great projecting lobes, slightly movable, beneath the thorax of the Zoea, and occupying a bulk nearly equal to that of the whole shield.

The circulation of the blood is beautifully clear. The pellucid colourless globules chase each other by starts to and fro, as the eye rests on the outgoing or returning current. It is distinct in some parts where you would scarcely have looked for it; as all over the lozenge plate of the tail, in the interior of the eyes, throughout the posterior spines of the shield, and the frontal spine. But besides, and apparently independent of, the circulation, there is a singular fusiform vessel in the latter segments of the abdomen, penetrating the tail-plate, on the ventral side. This vessel, now and then, at irregular intervals, dilates quickly and closes; the wave proceeding upward toward the head, but only for a short distance, and unattended with any impulse to the blood-globules. The nature of this vessel, and its use in the economy of the infant Crab, I can in no wise explain.*

For figures of these two forms the reader is referred to my Tenhy, 170, 172.

Chapter XII. Barnacles

You cannot have wandered among the rocks on our southern or western coasts, when the tide is out, without having observed that their whole surface, up to a certain level (often very precisely defined), is roughened with an innumerable multitude of little brownish cones. If you have ever thought it worth while to examine them with more care, you have seen that, crowded as they are, so thickly that frequently they crush each other out of their proper form and proportions, they are all constructed on the same model. Each cone is seen to be a little castle, built up of stony plates that lean towards each other, but which leave an orifice at the top. Within this opening, provided the castle be tenanted by a living inhabitant, you see two or three other pieces joined together in a peculiar manner, which are capable of separating, but which, when brought together, effectually close up all ingress.

Perhaps you have never pushed your investigations farther than this, having a courteous respect for the feelings of the inmate, which has prevented your intruding on a privacy so secluded. But I have been less considerate ; many a time have I applied the steel chisel and hammer to the solid rock, and, having cut off some projecting piece or angle, have transferred it, all covered with its stony cones, to the interior of a glass tank of sea-water, for more intimate acquaintance with the little builders, at my leisure.

These are Barnacles (Balanidce). Such a colony I have now in my possession, which I will submit to you ; for they present a beautiful and highly interesting spectacle, when engaged in their ordinary employment of fishing for a subsistence. And not only so, but I have living specimens of a much larger and liner species than the common one,—the Belanus ])orcattis, whose castle stands an inch or more in height. The structure, however, and habits are pretty much the same in both.

Without disturbing the busy fishers, then, just take vour seat in front of this tank, and, with a lens before your eye, watch the colony which is seated on that piece of stone, close to the glass side. From one and another, every instant, a delicate hand is thrust forth, and presently withdrawn. Fix your attention on some one conveniently placed for observation. It is now closed ; but in a moment, a slit opens in the valves within the general orifice, displaying a black lining with pale blue edges; it widens to an oval ; the pointed valves are projected, and an apparatus of delicate curled filaments is thrust quickly out, expanding and uncurling as it comes, to the form of a fan; then in an instant more the tips of all the threads again curl up, the threads collapse, and the whole apparatus is quickly withdrawn, and disappears beneath the closing valves. The next moment, however, they re-open : and the little hand of delicate fingers makes another grasp : and so the process is continually repeated while this season of activity endures.

Now, by putting this specimen into a glass trough, and placing it under a low power of the microscope, we shall see what an exquisite piece of mechanism it is. The little hand consists of twenty-four long fingers, of the most delicate tenuity, each composed of a great number of joints, and much resembling in this respect the antenna? of a Beetle. These fingers surround the mouth, which is placed at the bottom of the sort of imperfect funnel formed by their divergence. They resolve themselves into six pairs of arms ; for each one is branched from the basal joint, dividing into two equal and consimilar portions. Those nearest the mouth are the shortest ; and each pair increases regularly in length to the most distant, which are the central pair when the hand is extended. Each division of each of this longest and most extensile pair comprises, in the specimen before us, thirty-two joints, while the shortest consists of about ten, the intermediate ones being in proportion ; so that the whole apparatus includes nearly live hundred distinct articulations; a wonderful provision for flexibility, seeing that every joint is worked by its own proper system of muscles.

Moreover, every separate joint is furnished with its own system of spinous hairs, which are doubtless delicate organs of touch, since it has been established that the hairs with which the shelly coats of Crustacea are studded, pass through the substance of the latter, and communicate with a pulpy mass, richly supplied with nerves, which lines the shell.* These hair3 project at a more or less wide angle from the axis of the linger-like filament, and are graduated in length; and, what is very striking, as illustrating the exquisite workmanship of the Divine hand, the hairs themselves are compound structures ; for under a high power they seem to be composed of numerous joints,—a deceptive appearance, probably, what look like joints being rather successive shoulders, or projections outline,—while and con- HIND OF BABNACLE. strictions of the * "Pioc. Royal Society," ix. 215. O

each shoulder carries a whorl of finer spines, lying nearly close to the main hair, and scarcely deviating from its general direction. This barbed structure of the hairs is chiefly seen towards their attenuated extremities.

And now do you ask,—What is the object of this elaborate contrivance, or rather series of contrivances 1 I answer,—It is the net with which the fisher takes his food : it is his means of living. You have seen that the animal has no power of pursuing prey : he is immovably fixed to the walls of his castle, which is immovably fixed to the solid rock. He is compelled therefore to subsist on what passes his castle, and on what he can catch as he sits in his doorway, and casts his net at random.

You saw, also, with what a regular perseverance the casts were made ; and now that you have examined in detail the construction of the net, you are prepared to appreciate its fitness for the work assigned to it. Its extreme flexibility, produced by the number of its joints, enables the fingers of the hand, or the threads of the net (which you will), to stretch out and to curl up alternately, while the number of the spreading fingers enables the animal to grasp a comparatively large bulk of water in those curling organs. These, then, form a sieve ; the water passes through the interstices of the fingers, while the tiny atoms of solid matter, or the equally minute animalcules that constitute the food of the Barnacle, are sifted out, and detained by the fingers, which, curling inward, carry whatever is captured to the mouth.

But see how greatly the perfection of the instrument is promoted by the projecting hairs with which every one of the numerous joints is beset. These, standing out at right angles (or nearly so) to the direction of the finger, meet their fellows from the joints of the next finger, and, crossing their points, fill the interstices with an innumerable series of finer meshes,—meshes of such delicacy that it is next to impossible that any organised body inclosed in the given area should escape.

But there is more in them than merely this minute and wide-spread ramification. They are, as we have seen, organs of touch ; so that the net has not only the mechanical power of capture, common to an inanimate cast-net which a human fisher uses, but is endowed with the most exquisite sensibility in every part. The slightest contact of an animalcule in the inclosed water with one of those thousands of sensitive hairs communicates instantly an impression to the sensorium, and a consciousness of the fact to the Barnacle ; who is thus, without doubt, able with the quickness of thought to close the fingers together .at that part, and thus secure the victim.

To make use of the prey thus secured, the Barnacle is furnished with a mouth, which can be protruded into a sort of wart, and is provided with a distinct lip bearing minute palpi, and three pairs of jaws, of which the outer two are horny and toothed, while the innermost is soft and fleshy.

Fixed and immovable as the Barnacles are in their adult and final stage, they have passed by metamorphosis through conditions of life in which they were active, roving little creatures, endowed with the power of swimming freely in the wide sea. In this condition they present the closest resemblance to familiar forms of Crustacea, as you will perceive when you examine some specimens of the larvae that I am able to show you.

I have in one of my tanks an individual of the fine and large Barnacle, Balanus i^orcatus, which, for several days past, has been at intervals throwing out from the orifice of its shells dense clouds of atoms, which form compact columns reaching from the animal to the surface of the water. One of these cloudy columns, when examined with a lens, is seen to be composed of thousands of dancing creatures, resembling the Water-fleas that o 2 we lately examined. They maintain a vivacious motion,, and yet at the same time keep their association and the general form of the column.

Taking out a few of the dancing atoms, and isolating them in this glass stage-cell, we see that they have exactly the figure, appearance, and character of the young of the common Cyclops ; so that you would, without hesitation, if you knew nothing of their parentage, assign them to that well-known genus. Their movements are almost incessant ; a series of jerking progressions, performed by quick but apparently laborious flappings of the limbs, right and left together. They occasionally rest from their exertions for a few moments, but seem to have nopower of alighting on any object.

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