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their relation to the external pores is very remarkable. The formation of these organs is still entirely problematical. I have sometimes compared them to the cells full of needles of the Turbellarians, and to the stinging organs of the Acalephs, etc., but this is mere hypothesis.”

“ Tubular glands full of spherical granulations have been pointed out by us in divers Annelids. Sometimes they reach considerable dimensions, particularly among the Lycoridians, and in this case the glomration formed by the junction of glandular tubes was known to old authors and considered to be a sac. M. Quatrefages knew of one of the passages in which I had spoken of these organs, and cited an analogous observation of M. Keferstein, but by a singular blunder, he makes us describe circumvolutions of blood vessels when we spoke very positively of glandular branches (boyaux). . . .

Muscular system. The muscles of Annelids exhibit extraordinary varieties in their histological character. Sometimes they are composed of parallel fibres quite destitute of a nucleus, and at others of fibre-cells furnished with large nuclei. The existence of these fibre-cells of a muscular character in Annelids has been, it is true, denied by M. Schneider ; but “although this savant is right in the majority of cases, we shall see that the rule suffers certain exceptions in the pharynx of some Nereids, tentacles of many Terebellians, etc. Sometimes the muscular fibre separates into two distinct layers, one axial, the other cortical, as Leydig first observed.”

“The ‘Historie Naturelle des Annelés' describes between each segment a sort of tendinous raphis, in which the muscular fasciæ insert themselves. These raphids have no existence. It is easy in longitudinal sections of Annelids to see that the longitudinal fasciæ are continued without interruption the whole length of the worm. This is what Blainville, Della Chiaje, Rathke, Meckel, etc., observed. Muscular plates more or less complete, sometimes divide the previsceral cavity into several chambers. Thus the Ophelians, Polycirridians, and many Terebellians, the Aphroditians, and the majority of the wandering Annelids have three divisions in the perivisceral cavity, the Glycercians two, etc.”

Digestive Organs.-M. Quatrefages has endeavoured to establish a new nomenclature for different parts of the alimentary tube, the necessity for which may be disputed. Why, for example, in the Syllidians give the name dental region of the proboscis to the organ with glandular walls, which does not form part of the proboscis, and contains no teeth.* The

* In a note, M. Claparède says that M. Quatrefages has enumerated certain Syllidians as having tecth in this region, but has mistaken the species, which belong to quite diferent families.

names employed by other authors such as fleshy portion of the pharynx (M. Edwards), gizzard (Williams), proventriculum (Oersted), appear very preferable. Are there sufficient reasons for rejecting the names ventricle and glands of the ventricle, employed first by Rathke in reference to the Nereids, and repeated by his successors? Is it necessary to replace them by @sophagus, and salivary glands?... Salivary glands are usually more or less connected with the buccal cavity, while the glands in question are often twenty or thirty segments behind it. In certain Annelids the posterior region of the intestine following the biliary region, presents a special appearance. Its walls appear filled with cells containing curious concretions, without doubt destined to be eliminated with the fæces. I call this portion of the intestine the urinary region, though it does not appear to contain uric acid.”

The Perivisceral and Circulatory System.-- We owe to Quatrefages and Williams, especially to the former, a profound study of the perivisceral cavity and of the lymph which it contains. The perivisceral cavity is lined with a delicate membrane which is only demonstrable in large species, and which M. Quatrefages attributes the discovery of to himself. Had he searched the works of Della Chiaje and Rathke, he would have found the membrane and its name. The structure of this peritoneum (tunica sierosa, tunica peritonicale of Della Chiaje) is subject to great variation. In some species the perivisceral cavity is supplied with vibratile cilia borne by this membrane. Sharpey was, if I am not mistaken, the first to describe it among the Aphroditians, Williams afterwards observed it on the branchiæ of the Glycerians, and I described it throughout their perivisceral cavity. It was also noticed in the Tomopteridians. M. Quatrefages, who only cites en passant the observations of Williams, adds that this ciliary movement was known to him long ago in a number of Annelids, and that it may be seen in all species if any trouble is taken. This opinion is not correct. The immense majority of Annelids do not exhibit a ciliary movement in the perivisceral cavity, except at the entrance of the segmentary organs. I only know a perivisceral ciliation in the following groups :-all the Aphroditians, Glycerians, Polycirridians, Tomopteridians, and, lastly, in an abnormal TerebellaT. vestita. It is striking that all these Annelids, excepting the little Terebella and the Aphrodita aculeata, are totally destitute of vessels, and of these two exceptions, one, the Aphrodita, is an animal of rudimentary vascular system belonging to a vesselless family; the other, the Terebella, belongs to a family in general vascular, but of which, one tribe, the Polycirridians, is vesselless. In presence of these facts, I must regard the perivisceral ciliary

movement as a vicarious circulatory function in animals having no true circulatory system.” “ The circulation of Annelids is carefully described by Quatrefages, rendering full justice to the labours of Milne Edwards. It is to be regretted he has not shown the same favour to Rudolph Wagner, and Rathke. The distinction which he has established between arterial and venous currents appears to me very just in its leading features. Other authors have had similar opinions—witness the name Nervarteria, given by Della Chiaje to the ventral vessel, that is, to the aorta, in the sense of M. Quaterfages. The existence of blood corpuscles in the vessels of certain Annelids is now indisputable. M. Quatrefages admits three examples—the Glycerians, Phoronis, and Syllidians. In fact, among the first, the red corpuscles belong to the perivisceral cavity, and Phoronis scarcely preserves its place among the Annelids. But without speaking of the old observations of Rud. Wagner on a Terebella, confirmed by Kölliker, other examples might be cited. In this memoir blood corpuscles properly so called will be described in the Ophelians, Cirratuliaus, and Staurocephalians.

(To be continued.)

THE LUNAR ERATOSTHENES AND COPERNICUS.

JUPITER'S SATELLITES.--OCCULTATIONS.

BY THE REV. T. W. WEBB, A.M., F.R.A.S.

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BEFORE quitting the neighbourhood of the “rampart-work” of Gruithuisen, we shall briefly advert to the region lying W. of it. Here we shall find a deep crater Bode (28), nearly 9 m. in diameter, whose wall of go of luminosity makes it a conspicuous object. A smaller crater, Bode A, lying at a little distance N.W., is equally reflective. Close to Bode on the S. is an irregular ring, called Pallas, and at some distance W., and in the First Quadrant, another, Ukert, which the extreme influence of S.W. parallelism in its neighbourhood has squeezed almost into a square form, and rendered its aspect quite different at the first glance from that of Bode. At the foot of its wall on the S.E. is a straight ravine, wider than the generality of clefts, running in a S.W. direction. This I have seen interrupted in the middle by a broad, shallow valley, so as to make it appear like a cutting through the wide bank on either side.

The Sinus Æstuum (our H), as limited by B. and M. (who, unlike Lohrmann, have excluded from it the hilly region around Schröter) is a depressed, but considerably reflective surface, unique in its way, according to them, from the absence of the

VOL. XII. —NO. IV.

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slightest trace of a crater, as well as from its peculiarly level character; its smoothness being only broken by a few long but very low ridges issuing from Eratosthenes (29). The comparison of this district with one swarming with minute craters a little E. is extraordinary; and these forms, which would have been here most readily distinguishable, appear to be actually wanting. It must, however, be observed that their predecessor, Lohrmann, has delineated one very distinctly, of which, though his work was before them, they have taken no notice; and Mädler subsequently (1841), when in charge of the great Dorpat achromatic, perceived several not laid down in the map. Li's crater I found very conspicuous with 5 inches, 1861, April 18 and 20, May 17, as well as a second, and, perhaps, a third. These inconsistencies, but too frequently to be met with, introduce so much perplexity and obscurity into the question of lunar change, that we look forward with interest and pleasure to the survey now in progress under the auspices of the British Association, the results of which will certainly not be encumbered with similar ambiguities, at least on so considerable a scale.

Eratosthenes (29), a prominent crater, upwards of thirtyseven miles in diameter, and, therefore, equal in area to some of the smaller English counties, is, as our guides express it, the mighty keystone of the Apennines, and probably (as they think) the site of the outburst of that unknown violent agency which raised the summits of Bradley and Huygens. But for the nearness of the still more imposing Copernicus (30), it would certainly be the most remarkable feature of the neighbourhood. It is, however, very inconspicuous in full illumination. A great mountain occupies its centre, and the interior of the ring is supported by strong, broad terraces; the former, according to Schr., divides into two branches, and the latter, on the E. side, are in part separated by distinct ravines; a fact which deserves the attention of selenologists, as possibly throwing some light on the mode of their formation. The ring is brightest on E. Here its summit lies 15,800ft. above the gulf, while on the opposite side it only attains 10,900ft., that is, is only a little overtopped by our Etna! Schr. had given these measures consi. derably less, and probably too small. Lohrmann mentions two peaks, N.W. and S.W., the former the point of junction of the narrow prolongation of the Apennines; E. of this point he has placed a small deep crater on the top of the wall, which B. and M. have lowered to the inner terrace; he also speaks of several broad and generally parallel terraces descending as by steps on the exterior, and extending furthest S. The height of the wall from the outside is given by B. and M. as 3200ft. W., 7400ft. E., showing, with as fair a degree of accordance as

may be expected among such irregular surfaces, an interior depression of about 8000ft. This is something entirely unparalleled on the earth, and, at first sight, in connection with the vast extent and height of the ring, would seem to remove the phenomenon out of the reach of terrestrial analogy ; when, however, the very different amount of gravity on the Moon, and possibly a very different degree of resistance from cohesion, are taken into consideration, it does not seem necessary to abandon the idea of volcanic action.

On one occasion (1789, Sept. 12), when Eratosthenes was a little less than its own diameter removed from the terminator, Schr. observed that a zone forming the extremity of the shadow which then nearly filled the cavity, being the portion which lay on the interior slope of the ring, and, according to his figure, amounting to nearly £ of its whole extent, was noticeably less dark than the rest. This he supposed to be the effect of the commingling of the true shadow with the penumbra, or partial darkness, which arises from the apparent breadth of the Sun, and, therefore, borders every shadow in the solar system, where the Sun subtends a sufficient angle to make it perceptible. This is, of course, the reason why the shadows of all objects in terrestrial sunshine are ill-defined in proportion to their distance from the body which casts them; and this hazy-looking edge, which would be of great breadth on Mercury, where all the shadows would be extremely woolly, and imperceptible on Uranus, where they would be almost critically sharp, would, on the Moon, be sensibly equal to what we see on the Earth. But it is most improbable that such couid have been the cause of what Schr. observed. The lunar penumbra is, indeed, rendered visible as a narrow border* of diminished brightness where the terminator passes through surfaces making a very small angle with the rays of the rising or setting sun, while they are fully exposed to the direction of our sight; such as the grey levels of the M. Serenitatis, Imbrium, Vaporum, and others; or flat-topped elevations of any height; but where the surface is inclined towards the incident ray, as is evidently the case of the inner slope of a crater-ring after sunrise or (as in this case) before sunset, the penumbra could not possibly attain the projected magnitude described by Schr.t-Schmidt (who

* Schmidt gives its theoretical breadth 8" on the terminator; but practically it will be much less, as the diminished illumination would not be perceptible till a considerable portion of the solar disk was concealed.

+ On a former occasion the same observer has recorded a somewhat similar but much fainter grey border along the edge of the shadow, then become very narrow, within the crater Eudoxus (17). But in that case, being on the side of the cavity next the Sun, instead of the opposite, the appearance might be readily explained as a true penumbra, or illumination by a portion only of the solar disk, apparently enlarged and rendered more visible by its falling on the gentle slope of the foot of the wall.

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