intelligent, the most vigorous among the Invertebrata, such as the Spiders and the Insects, having no such simplicity of nervous structure, but only a series of centres, in the form of ganglions, more or less distributed through the whole body.

It must be borne in mind, however, that while, in the ROTIFERA, this brain is proportionally enormously large, and is quite alone there being no other recognized concentrations of nervous substance than can be dignified with even the title of ganglions, the neurine of which it is composed is in a very fluid condition; whence we may perhaps infer that its energies, whether for perception or will, bear no proportion to its volume.

Upon this great brain-sac, at the point that approaches nearest to the skin of the nape, but always with a forward aspect, there is seated a wart, often large and conspicuously hemispherical. The summit of this rounded eminence is crowned with a mass of red pigment, at times scarcely perceptible, then suddenly becoming visible like a flush of crimson, rich in hue, translucent, but sometimes pale and ill-defined. Upon this there lies a convex lens, which can, in many species -or, I should rather say, in many specimens of different species, for it is exceedingly variable and uncertain in this respect-be beautifully seen and clearly defined.

There is, in some species, a very curious and remarkable organ, in close connection with the brain, the use of which is altogether unknown. It is very distinct in this Eosphora and in Notommata aurita, and in one or two other species of the latter genus. It is a sort of globular sac, of large size, occupying the greater part of the bottom of the brain-sac, and sending up a rather wide tube through it. The globose extremity and a considerable portion of the tube are loosely filled with a substance, which, being opaque, appears dark when we view the animal by transmitted light; but when reflected light is brought to bear on it-a ray of the sun, for instance-it comes out quite white upon the general transparency. Ehrenberg assumes that it is of the nature of chalk, and so has called it kalkbeutel, or chalk-sac; but all that can with certainty be said is that it is a granular opaque white substance.

The appearance and motions of this organ and its contents add greatly to the interest with which the microscopist views one of these creatures. It is so unique, so unaccountable, so conspicuous, so beautifully defined, so evidently connected with the seat of intelligence, and with the most obvious organ of sense, that it exercises a kind of fascination on the observer, who is induced to watch it, and to linger upon it, in hope of solving the problems which it suggests. There, however, it

remains, unsolved as yet, an inviting fortress of research for daring young physiologists to scale and take.

Let me say what further I have observed on the matter. The sac itself is frequently drawn with force to one side or other, or down in the longitudinal direction, or across towards the breast. These movements are effected by means of slender muscle-threads, which are attached to it and to various parts of the body. The white substance lies in irregular masses in the sac, sufficiently solid to push out the elastic sides in wartlike knobs, but loose enough to allow the light to pass through the interstices as they move over one another. The walls of the sac are contractile; for we see its form change, and instantly some of the granules of opaque matter are forced higher up in the tube, rising and sinking by turns, like the mercury in a thermometer. Indeed, a thermometer, with its tube and its bulb, and their contents, affords a capital illustration of the whole organ. By means of their motions we are able to trace the course of the tube much farther than when it is empty, and to see that it passes to the front of the head, between the two frontal eyes, and, bending over with an arch, is lost somewhere in the ciliated face.

The transparent body is inclosed in an equally transparent skin, which is quite flexible, but apparently tough and strong, like wet parchment. It falls into transverse folds as the animal bends and wriggles from side to side, allowing much freedom of motion; and these folds have the additional advantage of allowing the body to be lengthened or shortened, at the will of the animal, at both ends; the skin becoming inverted at two or three points, when either the head or the foot is drawn in. Both these movements are almost every moment being performed, to a greater or less extent; and are quite distinct from the evolution and involution of the head itself, by which the rotating "ears" are suddenly turned out for swimming, or the contrary.

In all this order the muscular system is displayed with a clearness far greater than in any of the forms that we have yet considered. As might have been presumed from the untiring, vigorous, precise, and most varied motions of every part of these minute animals - motions which excite the admiration of the observer who remembers their dimensions, -the muscles are exceedingly numerous and well developed. In every species in which the viscera present the requisite clearness (for some are so constantly opaque, either from. the distension of the alimentary canal with food, or the successive growth of great turbid eggs in the ovary, that we can hardly discern any of the more delicate details of their internal structure), the great longitudinal and diagonal muscles are

seen, in the form of broad tapes running freely through the body-cavity, inserted at each end into some part of the skin by terminations more or less branched and divergent. Some of these pull the head down, or to one or the other side, or to the back or front; some, attached at the infoldings, produce the telescopic inversions; some draw in the different joints of the foot, or move the whole foot, or each joint, in various directions, or separate the toes.

Other muscles are seen in the form of slender elastic threads, of which there are very many, crossing the body in various directions, attached by expanding ends to the different viscera and serving to move them quickly and vigorously. There are also bands which go transversely around the body, no one band, however, completing more than a part of the circumference the action of these appears to be to narrow the breadth of the cavity, and so to protrude the extremities,either the head or the foot, or both at once. Minute and complex muscles are also present in the interior of the head, and in the mouth (mastaa) in great number, effecting the most precise and varied movements of these parts.

In order to render clear the form of the mouth in this order, I must again have recourse to a homely comparison. The parts, which, in the Builders,* I have endeavoured to illustrate by means of a cut apple and a set of pins, are all here, but they are so modified and changed in form and mutual relation that they can no longer be made intelligible by that device. Take away then the split apple, and substitute for it a pair of gardener's edging-shears, the blades of which stand in a different plane from the handles. Suppose there is but one handle (the pair being bound together, if you like), and the blades are hinged to its extremity so as to work while it remains fixed; now turn it up, so that the handle stands erect upon its top, and the blades work in the air nearly horizontally. If the blades were considerably widened, and curved downward at their tips like some surgical scissors, the resemblance would be perfect. These then are the lower jaws, technically termed the incus, the blades being the rami, and the handle the fulcrum.

Now then, for the upper jaws, we will again resort to the gardener's shed and rummage among his tools. We find a small digging-fork, such as can be used with one hand. It has three teeth, but that is of no consequence, for if it had but one, or any other number, up to seven or eight, it would still serve to represent the structure in some species or other. We take two such forks, and carry them away as lawful prize, in

* See "Popular Science Review," vol. i. p. 478.

the name of science. But these also must be modified a little. The prongs must be bent abruptly at about a right angle to the handle, where, however, a hinge-joint must be made, so as to allow this angle to be considerably varied. Now take these modified forks, and set them up one on each side of the blades of the shears, handles downward, at such a distance that the prongs shall just rest on each blade. These are the upper jaws, technically mallei, the prong part being the uncus of each, the handle the manubrium.

So we have the solid parts of this remarkable mouth. The prongs are fixed to the blades by elastic ligaments, so that when the former are drawn back the latter are stretched open, though both the blades and the forks have proper and independent movements, effected by means of muscles. The whole is contained in a three-lobed mastax, which does not importantly differ from that before described; and you may again have recourse to the parchment-covered cylinder of glass, to imagine the situation of the whole affair within the transparent body of the animal.

I have intimated that there is considerable modification in detail in these parts as found in different species. I have had specially in view Notommata aurita in my illustrative comparisons. In Eosphora, however, the blades are more pincerlike, coming together only at their tips, and the forks are but two-toothed, one tooth being more prominent than the other, and projecting over the blades, so as to cross with the tooth of the opposite jaw. In this, and in several other species, the mastax can be brought to the front of the face, so that the points both of the upper and lower jaws protrude; when so placed the animal frequently snaps them fiercely, and their close analogy with the two pairs of jaws in a carnivorous beetle becomes very evident; an analogy which, if we saw them only as they occur in many kinds of ROTIFERA, permanently inclosed far within the cavity of the chest, we could scarcely have imagined. It was this and similar observations which first compelled me to identify what has been commonly miscalled the "gizzard" in the ROTIFERA with the mouth and horny jaws of Insects.

The protrusion and snapping action of these two pairs of jaws are very strikingly exhibited by an attractive and beautiful race, the animals of the genus Synchata. These are mostly found in large collections of clear water, such as lakes and ponds and reservoirs; rarely or never in those minute stagnant pools and ditches in which many ROTIFERA delight. They appear to require a wide area in which to expatiate, and the element must be of the purest, or it will not do for Synchata. In such collections of water animal life is usually

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very scarce statements which we see hazarded in common compilations of natural history, and slavishly copied and recopied upon no authority, and with no test of their truth,that "millions of animalcules inhabit every drop of water that we drink;" that "all the waters on the earth are absolutely swarming with life," and the like, are gross exaggerations. I have often examined with care samples of water from different localities, and in particular that supplied to the inhabitants of London by the different water companies, and found scarcely a trace of microscopic life,-no Monads, no Euglena, no Infusoria of any kind, no Entomostraca, no ROTIFERA, with the exception of a solitary Synchata, or two, perhaps, spinning round, or two or three Polyarthra jumping hither and thither, in a whole tumblerful. Sometimes such water is a little more peopled than at others; but its tenants are always, as a rule, few and remote. Like most popular fallacies, the notion I allude to rests on a substratum of truth; there are waters of which it would be strictly true to predicate such facts; but they are stagnant collections, usually very limited in area, in which decaying organic matter, vegetable and animal, affords abundant nutriment, in consequence of which the increase of animalcules, both by generation and spontaneous division, goes on with almost inconceivable rapidity.

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To return, however, to our Synchata, the bright sparkling tenants of bright sparkling waters. They are comparatively of considerable size, several species being just discernible with the unassisted eye, in other words, being above onehundredth of an inch in length,-which, with a proportionate width, is about the limit of ordinary vision under favouring conditions. Their characteristic form is that of a boy's peg-top, especially if you select a specimen of the article with which Tommy Scapegrace has been for a week or two pertinaciously "digging" at his fellows' tops, by which means the iron peg has been driven further and further in, till only just the point projects then you have the Synchata exactly, the projecting point representing the minute foot with its tiny toes, which are commonly pressed together so as to look single. Now and then the animal rests on these united toe-tips, and rotates for several minutes, as if to maintain its character as a spinningtop; then away it shoots, and glides swiftly and giddily through the clear water by the hour together without repose; its enormous ciliary apparatus giving it great power of motion. The rounded front appears to be beset with cilia, but it forms a sort of indented crest or forehead, on which two antennæ are seated, as well as some pairs of curious stout branched bristles— whence the generic name, from oùv (sun), together, and xairn (chaite), a bristle-and which then descends on each side in