ordinary evolutions. They constantly keep up a series of swinging or balancing movements, sometimes rotating, sometimes forcibly driven in a certain direction, then in the opposite, yet no single one ever by any accident touching the walls of the capsule in which they are contained. If the capsule be ruptured, the motions instantly cease. These little bodies are of a calcareous nature ; and they are called otolithes* that is, ear- stones. The most that we know of these curious capsules, which are indubitably ascertained to be organs of hearing, we owe to the observations of the eminent zoologist just named, and of this you may perhaps like to learn a little.

Siebold says that a concentric depression is evident in these otolithes, and that there may be seen in the centre of the greater number of them a shaded spot, or rather a minute aperture, which penetrates through the concretion from the one flattened surface to the other. Subjected to a strong pressure, the otolithes crack in radiating lines, separating often into four pyramidal pieces. This separation also ensues, after a longer time, when the otolithes are immersed in diluted nitric acid; and, if we touch them with the concentrated acid, they suddenly dissolve with the disengagement of a gas, whence Siebold concludes them to be composed of carbonate of lime. The size of the otolithes is not equal, and in the same capsule there are always some which are smaller than others. Within the capsule they have, during life, a very remarkable, and in some respects peculiar, lively, oscillatory movement, being driven about as particles of any light insoluble powder might be in boiling water. The otolithes in the centre have the appearance of being pressed together so as to form a sort of solid nucleus, and towards this centre the otolithes near the circumference seem even to be

From the Greek ovg (ous), genitive Cjtoq (otos), an ear, and \i6oq (lithos), a stone.

violently urged, their centripetal rush being invariably repulsed, and as often driven again into a centrifugal direction. Removed from the capsule, the motions of the otolithes instantly cease. The cause of these curious oscillations remains undiscovered. Siebold could detect no vibratile cilia on the surfaces of the capsule, and the cessation of the motion when the otolithes are removed, proves them to be unciliated themselves, and, at the same time, distinguishes the motion from that of inorganic molecules.

It has been, however, more recently ascertained that the movements of the otolithes are due to very minute cilia with which the interior surface of the capsule is covered. This had been long suspected, and some eminent 23hysiologists, as Wagner and Kolliker, have distinctly seen the cilia themselves.

If you ask what can be the use of ears to a class of animals which are invariably dumb, I answer that though this is true with respect to the great majority, yet it may be only that our senses are too dull to perceive the delicate sounds which they utter, and which may be sufficiently audible to their more sensitive organs; and besides, some Mollusca can certainly emit sounds audible by us. Two very elegant species of Sea-slug, viz., Eolis punctata, and Tritonia arborescens,* certainly produce audible sounds. Professor Grant, who first observed the interesting fact in some specimens of the latter which he was keeping in an aquarium, says of the sounds, that " they resemble very much the clink of a steel wire on the side of the jar, one stroke only been given at a time, and repeated at intervals of a minute or two; when placed in a large basin of water the sound is much obscured, and is like that of a watch, one stroke being repeated, as before, at intervals. The sound is longest and oftenest repeated when the Tritonia) are lively and moving about, * Now called Dendronotus arlorescens.

and is not heard when they are cold and without any motion ; in the dark I have not observed any light emitted at the time of the stroke ; no globule of air escapes to the surface of the water, nor is any ripple produced on the surface at the instant of the stroke ; the sound, when in a glass vessel, is mellow and distinct." The Professor has kept these Tritonire alive in his room for a month, and during the whole period of their confinement they have continued to produce the sounds with very little diminution of their original intensity. In a small apartment they are audible at the distance of twelve feet. " The sounds obviously proceed from the mouth of the animal ; and at the instant of the stroke, we observe the lips suddenly separate, as if to allow the the water to rush into a small vacuum formed within. As these animals are hermaphrodites, requiring mutual impregnation, the sounds may possibly be a means of communication between them ; or, if they are of an electric nature, they may be the means of defending from foreign enemies one of the most delicate, defenceless, and beautiful Gasteropods that inhabit the deep." * * "Edinb. Phil. Journ.," xiv. 18G.

Chapter IV. Sea-mats and Shelly Corallines

When we were at the sea-side last summer we bought, you may remember, of a poor widow whom we met on the beach, a little basket of dried sea-weeds.

Now all of those objects were not sea-weeds. I mean they were not all plants ; some of them are animals, and these I wish to bring under your notice this evening for our microscopical entertainment. Here are exquisitely delicate crimson leaves, as thin or thinner than the thinnest tissue paper, with solid ribs and sinuous edges. Here is a tall and elegant dark red feather, quite regularly pinnated. Here is a tuft of purple filaments as "fine as silkworm's thread." And here is a broad irregular expanse of the richest emerald green, crumpled and folded, yet as glossy as if varnished.

Well, all of these are plants, certainly : they are veritable Algce, or sea-weeds. But here are other plant-like objects of a pale brown, drab, or snowy-white hue. Let us take this flattened brown leaf, divided into irregular broad lobes; it looks almost like a thickish paper, and is about as flexible. But pass your finger over it, and you feel that its surface is evenly roughened ; and on close and careful scrutiny you discern, even by the naked eye, that its surface is covered with a delicate network of minute shallow cells.

" Broad Hornwrack," and " Leafy Sea-mat," are the names which the old collectors gave to this object ; and ^modern naturalists have given it the scientific appellation of Flustra foliacea, and arranged it in the class Polt/zoa, a group of animate beings, which have much of the form of Polypes, and much of the structure of Mollusks.

We cut off a little piece from the end of one of the lobes, and put this upon the stage of the microscope. We now see that the cells are disposed in nearly parallel rows ; but so that those of one row alternate with those of the next, quincunx fashion, the middle of one cell being opposite the end of its right and left neighbours; or like the meshes of a net. The cells extend over the whole leaf, and are spread over both its surfaces in this case ; the united depth of two cells constituting the thickness of the leaf-like structure. There are other species, more delicate, which have but a single series of cells, all opening on the same side of the leaf.

Each individual cell is shaped like a child's cradle; and if you will imagine 20,000 wicker cradles stuck together side by side in one plane, after the quincunx pattern I have just mentioned ; and then the whole broad array turned over, and 20,000 more glued on to these, bottom to bottom,—you will have an idea of the framework of this pale-brown leaf; dimensions of course, being out of the consideration. The number may appear somewhat immense, yet it is no larger than the ordinary average, as I will soon show you. I measure off a square half-inch of this leaf, which I carefully cut out with scissors; now with the micrometer count the cells in the square piece.—You find 60 longitudinal rows, each containing 28 cells, or thereabouts. Very well ; a simple arithmetical process shows that there are 1,680 cells in this square hal: inch ; or 6,720 in a square inch. Now this very specimen, before I mutilated it, contained an area of about three square inches ; which would give 20,160 cells. This is the number on one surface; the other contains an equal aiumber ; and thus you see that I have not exaggerated the population of this tiny marine city. This, however,, is by no means a specimen of unusual size.

These cells, which I compare to cradles, are of shallow depth, but the head part rises to a much greater height than the foot. All round this elevated portion the margin is armed with short blunt spines, two on each side, which stand obliquely erect, projecting outwards over the middle of the next cell, which thus, in concert with the spines of the cell on the opposite side, they protect.

If you search carefully over the mass of cells with this pocket-lens, you will perceive that on some of them areseated minute white globules, which look like tiny pearls. These are not placed in any regular order, two being sometimes found on contiguous cells, but generally thej are scattered at more or less remote intervals. If we now apply the microscope to these appendages, each globule is seen to be flat on that perpendicular side which faces the foot of the cradle ; and this flat side is a movable door, with a hinge along its lower edge. The door is of a yellow hue ; the globule itself being, as I said, of a pearly white hue.

This is all that we can see in this dried specimen ; but if we had been fortunate enough to examine it when first it was torn from its attachment to an old shell at the bottom of the sea, you would have seen much more. And what would then have appeared I will describe to you.

Suppose, then, that a coverlid of transparent skin were stretched over each cradle, from a little within the margin all round, leaving a transverse opening just in the right place, viz., over the pillow, and you would have exactly what exists here. There is a crescent-form slit in the membrane of the upper part of the cell, from which the semicircular edge, or lip, can recede if pushed from within.

Suppose, yet again, that in every cradle there lies a baby, with its little knees bent up to its chin, in that zigzag fashion that children, little and big, often like to lie in. But stay, here is a child moving ! Softly ! He slowly pushes open the semicircular slit in the coverlid, and we see him gradually protruding his head and shoulders in an erect position, straightening his knees at the same time. He is raised half out of bed, when lo ! his head falls open, and becomes a bell of tentacles ! The baby is the tenant-polype !

"This is a very amusing romance," you say. Nay, it is no romance at all. If you will excuse the homeliness of the comparisons, I venture to affirm that a personal examination of the creature itself would justify their correctness, and you would acknowledge that they could scarcely be more apt.

Moreover, the globular chambers show signs of life ; their front doors suddenly open, gape widely, and then

LEAFY SEA- MAT.

(A portion magnified.) shut with a snap ; and presently this opening and shutting is repeated. The meaning of this action you will better understand when you see analogous organs in

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