But now another man approaches the post, and unties the rope. Instantly the boat glides ahead, and continues to do so, urged by the repeated strokes of the oars, whose effect on the water in making currents is now slight and imperceptible. The reason of this is that the water is now a fixed body (or nearly such), and the force of the impact is mainly spent on the movable boat.

The Brachionus is the boat, its cilia are the oars, and its foot is the rope. As long as this last maintains its hold, the whole force of the ciliary stroke is spent on the water, and currents are the result ; but as soon as this hold is broken, the force acts on the animal (= boat), which is thus rowed rapidly forwards.

The use of the cilia in this latter case is obvious. They enable the little animal -to rove about at its wayward will ; and doubtless motion is as pleasant and necessary to it as to the fish in the sea, or to the bird in the air. But what is the object of their vigorous rotation, when the animal chooses to maintain a firm hold with its foot % What is the use of rowing a boat, if you do not choose to let go the painter 1

To solve this enigma, let us search up our little Brachion once more; he will not roam long before he settles soberly again. Yes, here I have him moored. Now, mark carefully the vortices, or whirlpools, which are so vigorously circling round the animal's front, and you will perceive that the movement is not a strictly circular one, but that each whirlpool has an outlet close to the cilia; for the accumulated and condensed particles of pigment, after many rotations pass off in an united stream between the two crowns, and go away horizontally in a line from the ventral side of the front. That is to say, each vortex pours off its accumulation at a point on the inner side of the ciliary circle, and the two streams, uniting, pass off from the lip of the shell, to be drawn in again, however, by-and-by, when the centrifugal force is exhausted.

Now this stream passes immediately over the mouth, which is an opening in the flesh of the front, forming a deep cleft on the ventral side, the lips of which, as also the whole interior of the tube, of which it is the orifice, are richly covered with cilia. A certain portion of the atoms are thus arrested by these cilia, and are hurled by their vibrations clown this gulf. Yet not all, nor nearly all; for the lips appear to possess the sense of taste, or of some modification of touch, which enables them to refuse or to receive the atoms presented to them, so that only such particles pass down the throat as are selected for food. Some of the atoms of pigment are admitted, and one of the most pleasing sights connected with these animals, is to watch the swallowing of coloured food, its reception into the singular sunken mouth, where the great powerful jaws act upon it: thence its dismissal through the gullet, where certain glands pour upon it their secretions, into the stomach, where other glands, answering to a liver, change it ; and thence into the intestine and rectum, until its indigestible portion is discharged through the cloacal orifice.

The object of the mingling of colour Avith the water in which these and similar animals are held for observation, was the tracing of the phenomena of digestion. And, indeed, it renders the whole process beautifully distinct; for, from the transparency of the tissues, the presence of the coloured pellet is everywhere recognizable, since it retains its form and hue under all its changes, clearly revealing to us the shape, dimensions, and directions of the various canals through which it passes; here and there diffusing throughout the viscus in which it is held a beautiful roseate hue, more or less deep, without, however, causing- it to lose its own definite outline.

Let me now direct your attention to the organs devoted to the seizing and mastication of the food. And the more, because the form of these organs in the Rotifera is quite peculiar, quite unlike what is found in any other class of animals; though the parts are essentially the same as those which we have already seen entering into the mouth in insects.

Removing the carmine-stained water, I put into the live-box a drop from a vase very rich in organisms of many kinds. Among these you see very numerous the mulberry-like clusters of that beautiful green creature,, Syncrypta volvox, which is now pretty generallyconsidered a plant ; though from its spontaneous motion, swimming evenly along, revolving on its axis as it goes, you would be inclined to asjree with earlier observers in thinking it an animal. These appear to be favourite morsels with the Brachion : one has already been devoured, and is quite visible in the alimentary canal, its brilliant green hue shining out through the translucent viscera and tissues. Others are approaching, "-;, and two or three are iust 0> now drawn into the vortex of the ciliary current. It is amusinff to see the manoeuvres which the J3rachionus makes to take his prey. I say manoeuvres ',. for there reallv •J seem to be perception and intelligence. The mode inwhich it directs its ciliated flaps towards the spot where a Syncrypta is whirling, or suddenly stretches forward to the extent of the long foot, as if it would seize the prey by force, seems to indicate a cognizance of its proximity; as do also, still more, the manner in BKAC'HIOXUS. which it depresses the liplike lobes of the rotatory organ on one side, when the prey is in the vortex on that side, and the eager haste with which it shrinks down into its shell the instant the little mulberry drops at length into the throat.

But now comes the tug of war; the black, millstone-

like jaws open wide, and stretch forward to grasp the little victim (which is still distinctly visible through the transparent tissues) : they touch the globular envelope, but cannot quite grasp it. The Brachion redoubles its efforts ; the jaws gape vigorously, but can only scrape the sides of the little globe, which at every touch slips away, the expanse of the jaws being not quite sufficient to embrace it.

At last the little animal becomes indignant ; the jaws no more endeavour to grasp, but with a very distinct and sudden upward jerk throw out the prey, which until now has been retained and pressed downward by the contraction of the sides of the sensitive throat. Strange to see, the little Syncrypta, after all its imprisonment and rough handling, is no sooner free than it whirls merrily away,, revolving as it pursues its even ciliary course, just as if no interruption of its freedom had occurred.

Meanwhile, however, better success attends the Brachion's hunting ; for a smaller globe has sunk into the throat, and passed with a gulp into the mouth between the gapingjaws; which instantly close upon it, and,working vigorously, bruise it down with a hammer-like action upon a sort of central table. After this process has gone on for a few minutes, the green mass, less perfectly denned than before, slips through a narrow postern-gate, along a short slender alley, into the digesting stomach.

But what sort of a mouth is this 1 It is inclosed within the tissues of the body, not very far from its centre, so that no part of it comes into contact with the external water, or even approaches any portion of the superficies of the body. It has been usual to call the great hemispheric bulk in which the symmetrical hammers work so vigorously, a gizzard ; but it is a true mouth, and the hammers are true jaws.

This form of mouth is termed a mastax ; it consists of a dense but transparent muscular mass, forming three lobes at its lower part, deeply cleft at the front of its ventral side, where the passage, which I have called the throat, but which is more correctly designated the buccal funnel, enters. Within this muscular bulb are placed two bent organs like hammers, called mallei, and a third central table, called the incus. The mallei approach each other dorsally, while the incus is placed towards the ventral side, its stem pointing obliquely away from the centre.

Each malleus consists of two portions, united by a free but powerful hinge-joint. The lower joint (manubrium) is shaped somewhat like a shoulder-blade ; and the upper joint (uncus)* is set-on at nearly a right angle to it, but is capable of considerable change of direction by means of its hinge. It consists of five or six finger-like teeth, connected by a thin web of membrane.

The incus also consists of several distinct pieces. The principal are two stout rami, resting on what appears, when you look at the back or belly of the animal, to be a slender foot-stalk (fulcrum). But when you get a lateral view, the foot-stalk is seen to be only the edge of a thin plate, to the upper edge of which are jointed the rami, in such a manner that they can open and close, like the blades of a pair of shears. Each ramus is a thick, threesided piece, with the upper side hollow, and the inner flat, and in contact with that of its fellow, in a state of repose. The uncus of each malleus falls into the concavity of its corresponding ramus, and is fastened to it by a stout triangular muscle, which allows some freedom of motion.

Many muscles are inserted into diflerent parts of these organs, and into the walls of the inastax, which impart various and complex motions to all the parts. Thus, as we have seen, they are adapted to the various functions of mouth-organs, those of grasping, holding, bruising, and chewing food.

The mallei correspond with the mandibles of Insects ;

The uncus of the malleus must not be confounded with the incus.

and the rami of the incus with the maxilla? ; while the walls of the mastax with the two edges of its orifice correspond with the mouth, with its labrum and labium.

It is true we are somewhat startled to find a mouth placed far down within the cavity of the breast ; but there are other forms in this class, some of which I may be able to show you, where the mastax has essentially the same structure, in which it is placed at the front margin of the body, from which SIOUTH OF BKACHIONUS. the jaws can be freely protruded. The difficulty will seem less if you weigh the following considerations :—

The integument in the Rotifera is very flexible, and, especially in the frontal regions, is extremely invertible. In those genera in which the mouth-apparatus can be brought into contact with the external water, it is ordinarily, to a greater or less degree, retracted within the body, by the inversion of the surrounding parts of the exterior ; while, in those genera in which it is permanently inclosed, analogy requires us to consider the condition as induced by a similar inversion, but of permanent duration. If we imagine the head of a softbodied Insect-larva retracted to a great degree (as is done partially by many Dipterous larva?), the skin of the thoracic segments would meet together in front, around a purse-like opening, which would be the orifice of such a buccal funnel as exists in most Rotifera. In the latter, it is the normal, or proper condition ; in the former, it is merely accidental and temporary.

We need not devote any more minute consideration to the digestive apparatus in our little Brachion, but there

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