shall see some of the stalks of the macerated hay, or floating portions of the semi-decomposed leaves, clothed with what appears to the naked eye to be a very delicate white mucor, or mouldiness. Such a fragment placed in the "live-box" of the microscope will not fail to present many groups of one of the most attractive of all the Infusoria, the lovely genus Vorticella. (See Plate I. Fig. 1.) A little bell of glassy transparency is affixed by a sort of nipple to a slender filament or stem, eight or ten times its own length. The bell has a broad and thick rim or lip, within which, on two opposite sides, are apparently two pairs of cilia,* which are sometimes withdrawn, sometimes protruded, and are vibrated with a rapid snatching motion (a). The result of this is very curious, for when any atom in the water is drawn near the bell-mouth, it is not driven away nor drawn in, but is whirled round in a continuous circle above either pair. This gyration may be seen above one or more pair, even when the cilia are so far withdrawn as to be invisible.

Within the glassy bell are seen many pellucid bodies, which are supposed to be numerous stomachs; these are continually changing their sizes, forms, and relative positions. In general, the animal floats loosely through the water, the thread fully extended, but rarely so straight as not to show slight undulations; the basal extremity of the stem is affixed to the support, and the bell slowly roams about, with the length of its tether for a radius, now turning its open mouth, now its sides, and now its foot to the eye.

On any shock, such as a tap with the nail on the stage or "live-box," instantly, with the quickness of thought, so

* The cilia are really placed in a complete circle around the bellmouth; and the appearance above mentioned is merely an optical illusion, dependent on the relation of these parts of the circle to the eye, as viewed in perspective.

that the eye can scarcely trace the motion, the long stem is contracted into a beautiful spiral (b), suddenly bringing the bell close to the point of adhesion, when it immediately, but gradually, uncoils to its full length. It does not seem alarmed by tapping, except when fully extended; for if we tap the box all the time it is unfolding, it does not shrink again, until it has reached its full extension, but then it does instantly. It frequently, however, springs back again, when partially uncoiled, of its own accord, several times in succession. Hence we may presume that the spiral contraction is the result of alarm; but that though alarm may be felt from the bell's contact with substances in the water, or from currents, &c., at any time, a shock or tap produces this effect only when the stem is tense, and capable of vibration. The whole of the actions of this little animal are very sprightly and elegant.

The ordinary increase of the animals of this class is by self-division. In the Vorticelle it takes place in the following manner: One of the full-grown bells begins to alter its form, becoming first globular, then a flattened sphere (c), presently a slight notch or depression is observed in the upper part of the outline, and it soon becomes apparent that this depression is a constriction extending all round, which gradually becomes deeper and more marked (d). As the two divisions become more separate each assumes an oval form, united at length to its fellow only at the base (e). At this time the motion of the cilia is plainly visible, forming a circle in each within the body, near the summit. As the process goes on, the connexion between the two is reduced to a mere point, and they become capable of separate motion, so far as to diverge and look in opposite directions; the point of union being the common stem (ƒ). At this stage we may observe that the bell which is destined to remain is open at the top, within which the ciliary waves are chasing

DIVISION AND MULTIPLICATION.

47

each other in continuous wheels, the other bell being closed at the summit.

But on the latter, which is ultimately to be thrown off, a new and highly interesting phenomenon appears. The cilia, which before the division had played around the mouth, have become obliterated, probably by absorption; the orifice at that extremity has closed up permanently, for this is to be the base of the new animal; and a new bell-mouth and a new wheel of cilia are to be formed at the opposite end, which at present remains attached to the common stem. The first indication we can detect of this new formation is a very slight motion in the water, a little quivering, around what we must as yet call the basal part. Presently there appear waved hairs, which seem very flexible, and the motion of which resembles that of a fringe of loose silk moved through water, an action very different from the regular waves of true cilia. These waving hairs increase rapidly in length, and in the vigour and rapidity of their undulations, which gradually become decidedly rotatory, producing at length strong currents in the surrounding water, and imparting a tremulous motion to the whole bell.

It is evident now that the separation is imminent, for the minute point of connexion cannot long withstand the rushing current of these rotatory paddles. At length the bell suddenly shoots away (g), gliding with great swiftness through the water, borne by its numerous paddles, and whirls about for a while in a headlong, giddy manner. At length it chooses a place of rest, becomes stationary, fixes itself by that end which had formerly been the mouth, but is now closed up, and presently begins to rise by the development of a slender stalk, which, though minute at first, quickly increases in length, until it attains the original dimensions. P. H. G.

(To be continued.)

PAPERS ON THE AIR AND SKY.

No. I.

THE OCEAN OVER-HEAD.

OUR Continental neighbours have often remarked that an Englishman always accosts a friend with some observation about the weather; "Fine day to-day;" "Very foggy;" "Not quite so cold as yesterday." And in a country like ours, where we have such incessant alternations, sunshine and shower, blue skies and black clouds, snow and driving hail, frost and burning heat,-in such a varied climate the practice is extremely natural.

Yet how few know upon what all these changes depend, and how few can trace to their origin the grander and rarer phenomena of the skies! Who amongst us can map out the prevailing courses of the wind, and tell the secret origin of the lightning-flash or of the many-coloured rainbow? How many can explain why on a clear winter night the northern horizon sometimes flickers with the brilliant aurora, or why at intervals from the ethereal heavens come down showers of hot metallic stones?

There are mysteries connected with these things that the loftiest human intellect cannot penetrate; and yet there is much which we can ascertain. To the man acquainted with meteorological science, each cloud has its peculiar interest; to him the shiftings of the weathercock tell a tale full of meaning; the silent dew and the loud-voiced thunder alike speak to him in tones of deep significance. Already we know much, and by-and-bye we shall know more; for it is one of the advantages connected with great truths that every one we master is not only a pleasant attainment in

GROVELLERS, MARINE AND ATMOSPHERIC.

49

itself, but a vantage-ground placing fresh treasures within our reach, and these sometimes richer and fairer than all former acquisitions.

Let us commence our survey with the air and its composition, and the application of its several constituents to the uses of man. The fact is, that enveloping this solid globe of ours are two oceans, one partial, the other universal. There is the ocean of water, which has settled down into all the depressions of the earth's surface, leaving dry above it all the high lands as mountain-ranges, continents, and islands. And then there is an ocean of air, which enwraps the whole in one transparent mantle. Through the bosom of that ocean, like fishes with their fins and whales with their flippers, birds and other winged creatures swim; whilst, like crabs and many shellfish, man and other mammalia creep about at the bottom of this aerial sea.

Until they are better taught, people are apt to regard air and all gases as something semi-spiritual, a link between the material and the immaterial. A good emblem of the spiritual they may be, but nothing more. The natural philosopher knows them to be as really matter and as capable of being weighed, measured, and examined, as water or hard rock. The chemist knows that there are various sorts of air; and in the atmosphere he recognises a highly compound substance. If we ask him of what it is composed, he will tell us it is a mixture of several gases, oxygen and nitrogen, with very varying proportions of the vapour of water, and small quantities of carbonic acid and ammonia, besides traces of nitric acid, and of every other gas or vapour, noxious or pleasant, which from the many scented herbs and flowers, from the stagnant marshes or the fiery volcanoes, and from a thousand other sources, find their way into, and are lost in, the vast ocean above us: just as we may suppose that the sea will contain traces of the acids, and other salts, and