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give off a series of delicate branching filaments termed setæ. These are as transparent as spun glass, and add greatly to the beauty of the antennæ. The inferior or smaller pair, which have their origin behind the first, are considerably shorter, have fewer divisions, and are much less elegant. In the males the form of the antennæ is somewhat different, and serves to distinguish the one sex from the other. They are less elegant in their outline, are also shorter and thicker, and swell somewhat towards the tips, which end in a hinge-joint peculiar to the male (fig. 1). The mandibles, foot-jaws (the latter being so named from partaking of the character of both feet and jaws), the mouth, and first pair of feet are all included within the protecting compass of the first shield-shaped segment. The remaining divisions include the swimming-feet, viscera, and reproductive organs.

The general form of the Cylops quadricornis is ovoid or club-shaped, being broad and rounded at the head, with a gradual tapering off towards the tail, which ends in two long lobes, embellished with delicate transparent setæ of unequal length; thus forming an elegant plumose termination to this end of the body.

In its progress through the water the Cyclops moves with a rapid jerking motion, which may be very well observed by placing the animal between the eye and the light. It will then be seen that its principal propelling organs are its oar-like feet, of which it has five pairs. Each foot, which may be said to be double, consists of a common stem, from whence arise two jointed branches, which are liberally supplied with setæ, or bristle-like appendages. The fifth pair are, however, rudimentary, and in the two sexes differ in form.

From the abundance of this little animal in every stagnant pool and ditch, we may naturally infer that its mode of increase must be exceedingly rapid. The pond from whence we obtained our supply seemed to be literally alive with Cyclops and Water-fleas. In the former the females greatly preponderated, and could be easily distinguished from the males by their external ovaries, which hung suspended on each side of their bodies like miniature clusters of grapes. The number of eggs contained in each ovary varies from thirty to forty. Jurine, who made a careful calculation to show the wonderful fecundity of this species, reckons that one female in the course of twelve months would become the progenitor of 4,442,189,120 young. As it does not appear that the eggs increase in size while in the external ovaries, although they undergo a change of colour, and as experiments have shown that they retain their vitality even when the parent has been killed, most naturalists are disposed to consider this crustacean as oviparous. Nothing can be more unlike its parent than the young Cyclops when it first escapes from the ovary (fig. 2). Indeed, so great is the dissimilarity, that the older naturalists were deceived, and formed these imperfect individuals into a distinct genus, although Leeuwenhoek had previously pointed out their true relationship. In the early days of our microscopic inquiry—why should we be ashamed to confess it—we fell into a similar error; and no one, we believe, unless he had carefully watched the Cyclops from its birth to maturity, would ever have suspected the parentage. From the observations of Baird and others, it appears that a period of seventeen to twenty days is required to perfect the form of the young Cyclops. During this period it moults three times; at every moult it assumes a form more approximate to its parent. In getting rid of its cast-off clothes, it sometimes falls a victim to the process. These exuviæ, however, are most beautiful objects when seen by the microscope, presenting, as they do, a perfect cast of the creature's form, with all its articulations and delicate plumose setæ entire. It is always desirable to mount these casts permanently, as they form instructive objects, showing the gradual approach of the Cyclops towards its perfect state or form. Perhaps the best method of permanently preserving such objects is to soak the object itself for a few days in glycerine; then place it with some of the fluid in a cell formed of Brunswick-black, and hermetically seal a thin glass cover over it with gold size. If the angles between the cover and the cell are gradually filled up with the Brunswick-black, the preparation will keep for years. The Cyclops, though exceedingly rapid in its increase, is thoroughly kept in check by the numerous enemies which surround it on all sides. Millions fall victims to trout and other kinds of fish; and the delicious, delicate flavour of the former is said to be in a great measure owing to a plentiful supply of this living food. The Hydræ, and the larvæ of aquatic and land insects, all play their part in the work of destruction, and thus lend a helping hand in keeping down that teeming abundance of life which would otherwise choke up our ponds, ditches, and streams, with animal life, until existence under such circumstances would become an impossibility.—T. K.