demonstrated. In some groups, they elude our research, perhaps from their extreme delicacy; in other groups, as the rotifera, the minuteness of the animals themselves renders the detection of such organs almost hopeless. And, although Ehrenberg considers that he has succeeded in discovering, not only nervous filaments, but even nervous ganglia, there is perhaps reason to suspect that he may have been misled by appearances. We do not mean to say that nerves do not exist in these animalcules, for many things render it most probable; but merely that it yet remains to be demonstrated that the filaments described by him are such. We shall again advert to this subject. The great division, called Nematoneura, includes several classes, as bryzoa or polypes, with ciliated arms, external parasitic animals, termed Epizoa; cælelmintha, or certain intestinal worms; star fishes and echini; and the subjects of our present observations, the rotifera. The rotifera, or wheel-bearing animalcules, are so termed, from the appearance of certain wheels often seen rapidly rotating, in various situations on the anterior part of the body near the mouth. We say wheels; because they were so regarded by the earlier microscopic observers, who seeing them rotate, as it appeared, with great velocity, were completely at a loss how to account for their presence and motion, or to conceive of the nature of their organic union with the body of the animal itself. It scarcely need be said that the continued revolution of any part or appendage of the body, round an axis, (as a wheel turns on its axle,) is quite inconsistent with the possibility of an organic union of such an appendage to the body: this, indeed, was felt by the earlier observers, yet they saw the wheels of these animalcules whirling round and round, and were unable to solve the enigma which com pletely puzzled them. Vicq. d'Azyr, M. Datrochet and others proposed an ingenious solution of the difficulty; they considered each wheel to be composed of an exceedingly flexible structure, and that, while in reality stationary, it became thrown into a series of undulations, or alternate elevations and depressions by the action of muscular fibres; the elevated portion sinking, the sunk portion being raised, and so on in succession with great rapidity round the ring, as wave follows wave: the rapidity of this alternation of elevation and depression, which would certainly produce the appearance of a ruffled stream running along and returning into itself, may, as they suppose, so deceive the eye as to give the appearance of a revolving wheel. It is, indeed, true, that the rotation of these wheels, is an optical delusion; but, beyond this, it is now proved that there are really no wheels at all, and that the appearance of these is produced by circlets of minute cilia or fibrils, while the apparently rotatory motion in question is produced by a series of progressive undulations in consequence of the alternate and orderly extension and contraction of each separate fibril. According to the observations of Dr. A. Farre, (Phil. Trans. 1837,) the cilia, under a microscope of high powers, present an appearance of waves rolling round and round in a circle; each wave is produced by a number of cilia, those forming the highest point being at full stretch; the others, folded down upon themselves, in an increasing ratio to the middle of the interval between two waves, where they are most completely lowered: these, however, become in turn the most elevated, and those which were the highest, the most lowered, and so on in alternate succession, and with great rapidity, the waves appearing to roll onwards. The annexed diagram, allowance being made for its rudeness, will serve to explain the process. Fig. A. These cilia are certainly endowed with, by means of muscular fibres cc, voluntary motion; they are regulated in their actions by the will of the animal; they can be urged into movements of extreme rapidity, or put into gentle and tranquil action, or stopped in an instant. Sometimes, a portion only of the circlet of cilia is in action, while the other portion is quiescent, and sometimes a few cilia alone, are seen slowly bending and then stretching themselves; when all at once, the whole begin to work with the utmost energy, wave succeeding wave, with wonderful velocity. It is by the action of these cilia, that the animalcule rows itself through the water, and traverses the tiny ocean in which it revels, full of animation. They are not, however, exclusively organs of locomotion; they serve for the acquisition of food: fixing itself, by means of a pair of forceps, terminating the body, to some stationary object, (as, for example, an aquatic plant,) the animalcule sets its cilia in action, and thereby produces a whirlpool in the contiguous water, converging to the creature's mouth, and hurrying thither such minute particles, either of an animal or vegetable nature, as are drawn into the mimic charybdis. It appears that the cilia of these animalcules, whatever their own structure may be, are governed by a muscular apparatus, which is very conspicuous, and which retracts them, when not in use, within a kind of sheath, where they are safely lodged, till their action is required. Having thus explained the real character of the supposed wheels, whence this group of animalcules has received its general title, we may proceed to more particular details. The rotifera may be described as shell-covered animalcules, their body being inclosed in a moderately firm or horny investment, but of extreme delicacy, and very transparent, so that the internal viscera may be perceived through it. The upper, or free margin of this shell, is often indented, or ornamented with regular projections, and is continued by means of a fine membrane to the bases of certain elevations around the mouth, termed lobes, from which arise the cilia already described. See Fig. A. This membranous con tinuation of the shell does not confine the ciliary apparatus, but permits it to be retracted at pleasure within the shell, cilia themselves being drawn into the a The rotifera present great variations of form and colour; but all have at It has been already observed, that it is by the whirlpool which the action of the cilia produces, that aliment is brought to the mouth of these rotiferous animalcules. The mouth or oral aperture leads into a gullet, which varies remarkably in size in different species: in some, it is very capacious; but in others, as in Brachionus urceolaris, (fig. B,) it is a narrow canal. The gullet leads to a gizzard, or preparatory receptacle, (e), in which, by means of a curious apparatus, the food is either ground to pulp or cut in fragments. This apparatus is described by Ehrenberg as consisting of three teeth, which, by the action of the gizzard and of certain muscles belonging to them, work vigorously on each other, and so mince to pieces whatever is subjected to their operation. These teeth are three in number, as in this sketch, and con sist of one central and two lateral or superior ones: the central tooth is apparently fixed, and has two flattened facets on its upper surface, one for each superior tooth to work upon. Each of these superior teeth consists of two portions, namely, a basal portion, fixed to the walls of the gizzard, and serving for the attachment of muscular fibres, and a free moveable portion which may be regarded as the real tooth, while the other serves as a jaw. These free portions work with their inner edge upon the facets of the central piece, and this edge appears to be jagged or serrated, the better to tear the substances on which it acts. Minute as are these curious organs, the transparency of the rotifera, permits them to be dis tinctly seen, under a powerful microscope, which also demonstrates their effects upon the bodies of the smaller animalcules on which the various species prey; for, as with fishes, they are the food of each other, and the warfare is perpetually carried on. The hardness of these teeth, is not a little surprising; they may be detached from the body of the animalcule in a perfect condition, and be submitted by themselves, to examination beneath a microscope; they vary in minor particulars, as form and size, in every species; but their essential characters appear to be the same in all. From this teeth-furnished gizzard, or preparatory receptacle, a passage, varying in length in different animalcules, leads to the true stomach or digesting cavity, to which the food, after being subdivided, is conveyed. See F. in fig. A. and B. The form and the relative capacity of the stomach, like those of the gizzard, are very variable; but in all these rotiferous animalcules this viscus is furnished with certain appendages, which are regarded as being of a glandular structure, and destined to secrete a fluid essential to the performance of digestion. Ehrenberg considers them as analogous to the pancreas of the higher orders of animals, but without sufficient grounds. Professor Jones, on the contrary, believes them to be the first rudiments of a liver, or biliary apparatus, and we think this opinion much more entitled to assent than that of Ehrenberg: every analogy indeed favours it; and we know the liver to be "the most important and the most universal of the glandular organs subservient to digestion." We find an appendix supposed to represent the liver in insects; and in the mollusca and crustacea this organ is extensive, but of a rudimentary structure. In Brachionus urceolaris, (fig. B. gg,) this presumed biliary apparatus consists of two processes united to the upper portion of the stomach; but in Notommata clavulata, (fig. A. ggg,) three elongated sacculi are attached to each side of the stomach, and of these the uppermost on each side is the largest. Great, however, is the variation of these appendages as it respects form, number, and magnitude, in the rotifera; but they appear to be always present. We have already intimated that bands of muscular fibres have been distinctly But it is not only a nervous system which Ehrenberg believes that he has discovered in the rotifera, he also considers that he has demonstrated a vascular system, or an arrangement of vessels, for the circulation of the nutritive fluids of the animal structure, and he states that these vessels have a transverse course, running across the body; but it is difficult to imagine how he could distinguish between them and muscular fibres, running in the same direction; and indeed the probability is, that the vessels, as he conjectures them to be, are in reality muscular fibres, and not seen in these rotiferous animalcules: | organization. But, besides the bundles of muscular fibres thus presented, Ehrenberg states that he has been able to detect nervous filaments and even minute ganglia, or nervous centres, distributed in various parts of the body, but with a certain degree of regularity. The existence of distinct nerves and ganglia, supposing Ehrenberg to be correct, inasmuch as these organs would necessarily tend to elevate the creatures in the scale of animal life, leads us to receive with less astonishment a farther statement, given by this philosopher, namely, that the animals in question are not destitute of some of the external organs of the senses, and he believes that certain red or coloured specks, which he has observed above the region of the gizzard, are eyes; but he thus judges merely because these specks appear to be invariably connected with the nervous system. After all, it must be confessed that Ehrenberg's account both of the distinct nerves and ganglia, and of the eyes, in these animals is to be received with caution. That nerves exist, is indeed not improbable; but it does not follow that they have been detected. In conducting microscopical experiments, and especially with instruments of high powers, appearances are apt to mislead; and we are not aware that other naturalists have established by their own observations those of Ehrenberg, as far as relates to these important parts of veins or arteries. The existence of a true vascular system, supposes an according developement of the apparatus of respiration, and Ehrenberg regards a minute horny tube, found projecting in many species from the neck (fig. B. h) as serving for the admission of the surrounding water into the general cavity of the body, and also for affording it exit; and he thinks that the alternate contractions and dilatations of the body observable in the rotifera effect this aquatic res piration, the water being drawn in by the dilatations and expelled by the contractions; and he states that when the internal cavity is filled, the viscera are separated from each other so as to present clear and definite outlines, but that when the water is expelled, they approximate each other, and appear as a general indefinite mass. The water being thus admitted into the body of the animal, its decomposition, and the aëration of the circulating fluid, is effected by certain little vibrating points, or organs, attached to two undulating viscera, running down each side of the body; these little organs he describes as attached by a footstalk to the viscera in question, and to have their free extremity inflated, and perpetually vibrating. His first idea was, that they belonged to the vascular system itself, but subsequently he considered them as branchiæ, or internal gills, over which a mesh of exquisitely delicate vessels ramify. It is easy to perceive that there is more of theory, and conjecture, than of absolute demonstration in all this. But theory has its uses; it leads to farther inquiry, and prompts the endeavour either to confirm or confute it. The rotifera are oviparous; they produce eggs, from which the young are excluded, sometimes while yet within the body of the parent. The eggs of some of these animalcules, appearing like minute transparent globules, are calculated to be, when first deposited, only the twelve thousandth part of an inch in diameter; but they increase in magnitude, and then constitute most interesting objects of microscopic examination. In an egg of about the one thousand and seven hundredth part of an inch in diameter, the included animalcule may be distinctly perceived, even the actions of the cilia may be distinguished, producing the wheel-like rotatory appearance previously described. At certain times, the eggs may be easily recognized before being deposited by the animalcule, lodged in a long floating sac, in the cavity of the body, (fig. A. kk ;) for the transparency of the creature is such as to permit the minutest parts of its internal structure to be seen; but it often happens that the sac is empty. With respect to the frequency with which the eggs are produced, nothing appears to be positively ascertained. Such, then, is the general outline of what we know of the structure of the rotifera. They are active and vivacious creatures, and by the celerity and address of their movements, give delight to those who observe them. To see a shoal of them in a drop of water, avoiding each other, in their mazy courses, and performing a thousand mingled evolutions, is perhaps one of the most interesting spectacles which the reflective can contemplate; but this delight gives way to astonishment, or rather to meditation, when he perceives that these creatures are elaborately constructed; that they are organized with an express relationship to their destined mode of life; and that they enjoy their existence like the fishes of the sea, or the birds of the air, or the wild beasts of the desert. "It is delightful," says Sharon Turner, "to see by these miniature existences, small almost to invisibility, and by their careful organization, as finely contrived as that of the grandest creature, that greatness and littleness make no difference to Him in his creation, or in his providence; they reveal to us that magnitude is nothing in his sight, that he is pleased to frame and regard the small and weak, as benignly and attentively as the mighty and the massive. We are high and low, great and small, as to each other, but not to Him." It is plain and clear, then, that as respects any criterion of complication or refinement of structure, mere size, of all the circumstances attendant on organized beings, is of the least importance. Things animate or inanimate, are great or small only in our minds, only as tested by the operation of our limited and imperfect senses; but with reference to the operations of creative power, and in His sight, from whose all pervading scrutiny nothing is hidden, the distinctions of great and small vanish. With Him who is omnipotent, omnipresent, and eternal, number, magnitude, and time are as nothing; these are terms which have relationship only to ourselves. To frame the smallest animalcule with an organization more refined, more complicate than that of the hugest whale, requires but the fiat of God; and he counts the myriads beyond myriads, with which the waters of this globe are tenanted, though our minds recoil from the reckoning of the numbers which revel in a little space. Thus does nature, in the animalcules, which can be contemplated by us only through a powerful microscope, show forth the praise of God, and call upon us to adore his power, his wisdom, and his goodness. M. UNDESIGNED COINCIDENCES OF SCRIPTURE.-No. VII. LET us now contemplate David, yet upon his death bed, giving in charge the execution of his last wishes to Solomon his son. Probably in consideration of his youth, his inexperience, and the difficulties of his position, David thought it well to put him in possession of the characters of some of those with whom he would have to deal; of those whom he had found faithful or faithless to himself; that, on the one hand, his own promises of favour might not be forfeited, nor, on the other, the confidence of the young monarch be misplaced. Now it is remarkable, that in this review of his friends and foes, David altogether overlooks Mephibosheth, the son of Jonathan. Joab he remembers, and all that he had done; Shimei he speaks of at some length, and puts |