In this jar of fresh water, which has been standing in the window for weeks, you may see among the green filaments of Chara many little atoms, which scuttle hither and thither with a rapid succession of short leaps. These belong to the genus Cyclops, and are Crustacea, belonging to the order Entomostraca.

By the aid of a glass tube which I stop at one end with my finger, I will endeavour to catch one. It is no easy matter, as you see, for the instant the end of the tube is brought near to one, he takes the alarm and leaps nimbly away before I can make the water rush in by withdrawing my finger from the other end. But I have one at length.

Here it is ; a living atom, not more than a sixteenth of an inch in length, looking something like a pellucid egg, furnished with long antennas, with five pairs of branching feet, and a long tail terminating in bristles. But its parts and organs must not be dismissed in this •summary way ; we must look at them in detail.

And, first of all, in the very midst of its forehead, like that obscene giant* after whom our tiny friend is named, —it possesses a single eye that glares like a ruby. It would need no vast beam of olive-wood, sharpened and heated in the fire, and "twirled about" by the united strength of five heroes, to "grind the pupil out;" for though brilliant and mobile, it is far too minute to be touched by the tip of the finest needle. Yet it is elaborately constructed; for it consists of a number (not very large) of simple eyes placed beneath a common glassy cornea. Several muscle-bands are attached to this compound organ of vision, and are arranged so as to form a cone, of which the eye is the base ; these give the eye a movement of rotation upon its centre, which may be distinctly seen.

All the limbs, including both pairs of antenna*, two pairs of foot-jaws, five pairs of feet, and a pair of taillobes, are furnished, at each of their many joints, with tufts of long hairs ; these appear to act the part of paddles, as the active little animal strikes the water vigorously with all its limbs, for the purpose of progression ; and also for the creation of currents in the fluid ; which currents subserve a double object,—the bringing constant supplies of water to be respired, and floating atoms of food to be devoured.

In this individual, which is a female, the antenna? are nearly equal in size throughout their length ; but, in the male, the middle joints of the upper pair are remarkably enlarged, forming a large swelling, followed by a sudden contraction, the first part of which is hinged. All of the true feet and the second pair of foot-jaws are divided * Odyss. IX.

to the base into two equal branches, so that the animal seems to possess no fewer than twenty-six limbs : each of which being many-jointed, and each joint, as I have observed, being set with delicately-plumose hairs, the whole effect is most elegantly light and feathery.

On each side of the slender tail-like abdomen you see an oval bag, connected with the body by an exceedingly slender thread of communication, and tightly filled with pellucid globose bodies. Like John Gilpin, of equestrian fame, when " He hung a bottle on each fide To keep his balance true/' our little natatory harlequin "carries weight." But these bags are filled with eggs, a temporary provision for their due and proper exposure to the water, while yet they are protected from enemies. They are developed only at certain seasons, when the eggs, having attained a given amount of maturity in the ovary, are transferred through the exceedingly slender tube into these sacs ; and are there carried about by the mother until the young are hatched ; when the curious receptacles, being no longer needed, are thrown off, and speedily decay.

Here is a second form. It is named Lynceus, and is nearly as common as the Cyclops in our stagnant pools. Essentially its structure is the same ; but it has this peculiarity, that its body is inclosed within a transparent shell, which is thin and flattened sidewise, and through whose walls all the movements and functions of its parts are distinctly visible. The shell is broadly ovate in outline, comes to a sharp edge all along one half of its circumference, but is open all along the other; as if two watchglasses were soldered together, edge to edge, and then a portion of the edges ground away, so as to leave a narrow but long entrance. Through this narrow orifice the limbs are protruded for locomotion ; and through it the sur- N rounding water finds its way in currents, bringing oxygen to be respired and food to be devoured.

The translucent shell descends in front into a sharp long beak, below which are seen the organs of the mouth, two pairs of foot-jaws, beset with fine bristles. At the origin of the beak is the eye, consisting, as we saw in the Cyclops, of several lenses, enveloped in a common cornea, the whole forming a movable orsfan of a blue-black hue. Just behind this, at the very highest part of the shell, is a little colourless bladder-like vesicle, which constantlv maintains a rapidly alternate contraction and dilatation. This is the heart, and this motion circulates the blood.

Below this, there is seen a great translucent irregular mass of fle^h, evidently comprising many viscera, which winds along from one end of the shell to the other, nearly occupying its entire area. It is not in connexion with it at the hinder part, as we see by its free movements there, where it curves round, and, bending beneath, terminates in a blunt tail, armed with two strong hooks, which can at pleasure be thrust down through the narrow orifice of the shell, and become partially straightened by being forcibly thrown backward. This great central mass is mainly occupied by the alimentary canal, in which food in various stages of assimilation may at all times be seen, and in which the interesting function of digestion can be witnessed throughout, from the first seizure of the atom and its mastication by the jaws, to the discharge of the useless remains.

The individual before us does not carry at this time eggs in the process of development ; but the deficiency is supplied by a Daplinia which is playing about in the same drop of water. Here you perceive, between the arched outline of the shell and the sinuous outline of the free soft body, an open space of some size, which constitutes a receptacle, in which the eggs are deposited as they are laid, and in which they remain not only until the little animals are hatched, but until they have acquired a sufficient maturity to swim about and get their independent living.

This receptacle, in which you may see five or six eggs, is freely open to the surrounding water, which enters the slit edge of the shell behind the tail. Perhaps you wonder why the eggs are not washed out by the respiratory currents ; they are, in fact, maintained in their position only by a slender tongue-like projection from the back of the parent, which appears to have that special object. When, however, the young are ready for freedom, the

DAPHNIA.

mother has but to depress her body a little more than ordinary, when the door is opened, and the young easily slip from the receptacle into the open water.

These tiny odd-looking sprawling things that you see moving about by quick jerks in the same drop of water, are the young recently hatched. They are quite unlike their parent, having as yet no bivalve shell, no abdomen, and only three pairs of limbs. The body is a transparent plate, resembling the bowl of a spoon in form, but ending in two points which carry pencils of bristles. The large x 2

dark eye is conspicuous in front, and the six-jointed and bristled limbs radiate from the centre, projecting stiffly on all sides. The second and third pairs are seen to be double, each giving off a branch, which is pencilled with bristles like the principal stem.

We have not yet done with these tiny Water-fleas. The sediment at the bottom of this jar of water is quite alive with a host of nimble atoms, some of which you may see crawling up the sides of the glass. They are quite distinct from either of the kinds we have been examining, not only in details of structure, which is more identical, indeed, than it seems at first sight, but in habit; for, whtreas they shoot to and fro through the water with great force and rapidity, these can scarcely swim at all ; or, if they do, it is with comparative slowness and much apparent effort; though over the smooth side of their glass dwelling, or upon the stems of waterplants, they glide along with much ease and elegance by the quick vibrations of their pencilled feet.

The form we are now contemplating is distinguished by the name of Cypris, a genus which contains a good many British species. It is more completely inclosed in a shell than even the Lynceus ; and its envelope more truly resembles the shell of a bivalve Mollusk, for the valves are open for more than three-fourths of their circumference ; while the portion of the back that is united is sufficiently elastic to allow of some degree of expansion, thus answering the purpose of a hinge.

ISTow look at the elegant little creature. Its most prominent feature is its two pairs of antenna?, one projecting forwards and curved upwards, the other downwards. Both consist of several transparent joints, and are tipped with long clear bristles; but the pencils which tip the upper pair are specially graceful, being as long as the whole shell, exceedingly slender, beautifully curved, and so transparent that they seem formed of spun glass.

Another peculiarity is, that there seems to be but one pair of legs, which terminate each in a hooked spine. You now and then see these awkwardly thrust out from beneath the hinder part of the shell, but locomotion is principally effected by the pencilled antennae. There is, however, a second pair of legs, but these do not usually make their appearance outside the shell, being curved backwards to sustain the ovaries.

CTPRIS.

Early in the present century, an Irish naturalist, Dr. J. Vaughan Thompson, announced a discovery, which, upsetting conclusions previously received by all, caused no little dissent and opposition, and gave rise to a lengthened and wide-spread controversy. A very minute crustaceous animal was known as inhabiting the open sea, to which the name of Zoea had been given. It had sessile (i.e., not stalked) eyes, and was remarkable for having a long spine projecting from the face, and a similar one standing up from the centre of the back. Another form was known, which constituted the genus Megalopa ; in which the body was broad, the eyes stalked, and the abdomen projecting behind. This was also small, but somewhat larger than the preceding.

Xobody suspected that these were other than inde-

pendent forms of animal life, distinct from each other, and equally distinct from every known genus of Crustacea besides. It was supposed that no animal of this class underwent metamorphosis, or that change of form in different periods of life which distinguishes Insects ; but that these creatures retained through life the general shape, slightly modified by development of parts and organs, which they each displayed when hatched from the egg.

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