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not presenting any appreciable structure. At the close of a variable time the branchia contract, although no muscular fibres can be distinguished. The ampullæ empty themselves, and sometimes completely disappear. The blood runs by the central canal of the branchiæ, and arriving at the base of that organ, passes into the efferent vessel. In this return movement it necessarily meets with the venous blood, and must mix with a certain quantity of blood which has not been subjected to the action of air." Bearing in mind this radically false description, let us see how the normal circulation takes place in the branchia of an Annelid. There cannot ordinarily be any mixture of arterial and venous blood. In fact, the artery goes to the extremity of the branchia, where it turns upon itself to return as a vein. Vein and artery are exactly parallel to each other. Throughout the whole length of the branchia these two vessels are placed in communication by a double series of vascular loops, which pass into the subcnticular layer, and which offers the greatest facility for the action of water charged with oxygen, through the very thin cuticle. As for the contractility of the pretended ampullæ, there is nothing of the sort. Certain genera, like the Terebellians and Telethusians, for example, exhibit many rythmical contractions all through the branchia, but not of the vessels themselves. Moreover, this fact is exceptional. In the family of the Serpulæ only do the branchiæ exhibit even a remote resemblance to the description of M. de Quatrefages. In fact, in these Annelids the artery is continued directly into the vein at the base of the branchiæ, and from this point of reunion a single vessel proceeds, which penetrates the branchia, and sends a cæcum into each branchial branch. But M. Quatrefages describes in the secondary branches of the branchiæ of the Serpulians an apparatus of ampullæ, of which no trace exists. The blindvessel exhibits no ramification, it is simply cylindrical and contractile, as described by Grübe and Kölliker. In their branchiæ, the blood exhibits an alternating movement, which is exceptional. In all the other families the branchial circulation is continuous in one direction. Blind vessels with alternating circulation, are found in the tentacles of Spiodians, Amphictenians, and Pherusians; in one part of the so-called branchial threads of Cirratulians, but these organs are not respiratory (unless, perhaps, lymphatic). [M. Claparède then remarks on the way in which M. Quatrefages was misled, and observes that the point was cleared up thirty years ago by Grube.]

"Reproductive Apparatus.-The reproductive apparatus of Annelids remains very imperfectly known. It is true numerous works have thrown fresh light upon the educatory

organs known, since Dr. Williams described them, under the name of segmentary organs; but our knowledge of the sexual glands has made little progress for the last thirty or forty years. This memoir will, I hope, make these organs, in a great number of species, sufficiently known."

M. Claparède then remarks on the very inexact description of M. Quatrefages, and continues :

"The distribution and conformation of the sexual glands of Annelids is subject to numerous variations, which will be illustrated by numerous examples in this memoir. The following may, however, be regarded as the most widely diffused. The sexual glands form more or less complex clusters or interlacements of cords, of which the axes are occupied by sanguiferous branches, often contractile. The sexual elements, when growing, form ruffs round the vascular axes, and develop at the expense of a layer of nuclei close to the vessel. With certain vesselless Annelids this form of sexual gland is preserved, but the axis is occupied by a solid cord, instead of a vessel. Among the females, the ovules are often in close juxtaposition in the ovary; sometimes, however (Owenia, Della Chiaje, and certain Polynoe), each one is inclosed in a special ovisac. In either case the eggs, on arriving at maturity, detach themselves from the ovary, either directly or indirectly, through rupture of the ovisac. The zoosperms detach themselves from the testicle to float freely in the perivisceral cavity. Doubtless this fundamental form is sometimes subjected to important modifications, to constitute, for example, the peculiar sexual tissue of the Nereidians, or the floating testicles of the Dasybranchians, which will be specially described. The eggformation of the Terebellians and Serpulians is still more divergent, but we always find a cellular tissue, fixed, or composed of floating materials, in the midst of which the sexual elements are developed.

"The sexual glands have long been recognized in many Annelids, but these old observations have been partly forgotten. Thus, while Pallas erroneously supposed the eggs of the Aproditians to originate in the liquid of the perivisceral cavity, Gott, R. Treviranus and Della Chiaje recognized the true ovaries at the base of the feet of these worms. . . . Even the existence of a sanguiferous vessel in the axis of the sexual glands was not unknown."

M. Claparède points out the errors of various authors, and adds::

"It is indubitable that Annelids exist which are destitute of segmentary organs, or in which they are reduced to simple openings in the back of the body.

"Nervous System.-It is, without doubt, to M. Quatrefages

and M. Leydig that we owe the best researches into the nervous system of Annelids. The first chiefly directing his attention to the external form of this system, and the second to its histology. . . . M. Quatrefages has been so fortunate as to find a stomato-gastric system of nerves, similar to that of the Hirudinea. I have not been able to recognize it, but I am sure that a negative result is not of great importance in these difficult investigations. I am, however, astonished that the combined efforts of other observers have been equally unsuccessful. . . . The structure of the nervous system varies astonishingly in the series of Annelids; the distribution of nerve-cells particularly being subject to a host of variations, which will be explained hereafter. In the ventral chain the cells belong chiefly to the surface and the sides, as Leydig has already noticed. The existence of large tubular fibres on the dorsal surface of the nervous chain, so general among the Oligochata, is confined among the Polychata to a small number of families (Capitellians, Aricians, Spiodians, Syllidians, Eunicians), and even appear in some representatives only of these families.

The nerve terminations amongst the Annelids have only been studied hitherto by myself, and by MM. Keferstein and Kölliker. All these terminations appear related to the functions of touch. The nervous expansions of the organs of sight and hearing are little known, even in Alciope, notwithstanding the researches of Leydig. In reference to this subject, I may recal an opinion of Joh. Müller, which has fallen into oblivion. We owe to this great physiologist an excellent figure of the central nervous system, and of the eyes of the Nereids-a figure to which his successors have not added anything important. He does not consider the organ called a crystalline lens as a dioptric medium. He denies its transparency, and regards it only as a terminal enlargement of the optic nerve. Although the transparency of the crystalline body is in many cases incontestible, the opinion of Müller on the functional value of this organ should not be rejected. The eyes of Nereids and of most other Annelids appear destitute of all apparatus for accommodation. Admitting that the percipient elements are lodged between the granules of pigment, it could be only objects at a determinate distance that could project their images upon this choroid pigment, and the sight of the creature must be very limited. This difficulty disappears if we seek in the crystalline body at once a refractory medium and a percipient organ, as we are almost obliged to do in the crystalline cones of the Archropoda.

Restoration of Mutilated Parts.-The observations of Bonnet on the restoration of mutilated parts among the earth

worms, confirmed by Lyonnet, Réaumur, Dugés, etc., were timidly questioned by Vandelius, and by Bosc, and more recently and positively by Williams, Vogt, and others. We must, therefore, be thankful to those who called attention to early observations, like Baird, or made fresh experiments, like Quatrefages.

The restoration of mutilated parts of Annelids is incontestible. Many of them can reproduce even the anterior region with the head. Amongst recent authors, M. de Quatrefages has demonstrated this fact over again in Eunice, and Dalyell followed step by step the reproduction of the head and branchia by the posterior extremity of a Sabella. I have also met several times with marine worms (Eteone, Nepthys, etc.) which have undoubtedly reproduced their anterior region, the restored portions being distinguished by lighter colour and smaller diameter. The aspect of these worms resembles that of the Heteronereids; so great is the difference in the two regions, one would think they were two portions of different worms stuck together. One interesting remark occurs with reference to this subject: If a worm is severed transversely, does the posterior part always reproduce exactly the number of segments in the suppressed anterior portion? It is probable. At least I met with an Eteone which reproduced an anterior portion of nearly fifty segments. The head is undoubtedly the first to be formed, and then fresh segments are successively produced at the junction of the old part and the new. This, however, requires to be supported by positive observations.

Geographical Distribution of Annelids.-In this section M. Claparède disputes the accuracy of M. Quatrefages in limiting the locality of species. M. Quatrefages does not admit, for example, that the Mediterranean and the ocean can be inhabited by the same species, and sometimes makes specific distinctions out of the fact of locality only. He also maintains that littoral species cannot live under such changes as the presence or absence of tides. At Naples, however, M. Claparède kept littoral Annelids for months in captivity, and found the best mode of making them prosper was to deprive them of water for some hours each day, in order that the vessel might be oxygenated.

Classification.-On this subject M. Claparède remarks that we are approaching a natural classification, and that the families now established are for the most part well founded. He does not propose any new families.

VOL. XII.-NO. V.

BB

LUNAR DETAILS.-DOUBLE STARS.-CLUSTER AND NEBULE.-TRANSITS OF SATELLITES.-OCCULTA

TIONS.

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

MUCH of the story of Copernicus remained untold when we broke off last month, and what we have already heard may well give us an interest in the remainder. It will be matter of familiar observation how striking is its aspect under very varied angles of illumination-how the magnificence of its broad and massive wall, and the extraordinary roughness of its glacis, as it rises upon the terminator, give place to a relief in higher sunlight which exhibits the serpentine terraces, the central elevations, and the whole arrangement of the structure in a more intelligible manner; and how this aspect is again gradually replaced under increased illumination by one of more delicate but still very expressive relief, and of considerable permanency; I have seen a little true shadow cast from the great peak in the W. wall, and from a steep terrace on that side, as late as 3d. 14h. before Full Moon. The beauty of these very dissimilar, yet intimately related aspects must be seen, and studied, to be fully appreciated. Mention ought to be made of a very striking engraving proceeding from the Collegio Romano,* as exhibiting the latter of these positions on a large scale, and with much cleverness of effect as well as fullness of detail, but, we are obliged to add, some degree of inattention also. We shall, however, proceed at present with an abstract of the remarks of B. and M. on its immediate vicinity. It is enclosed by a great mass of closely crowded mountain chains, arranged in lines partly radiating, partly parallel to the ring, especially on E. Here many of them are of very slight elevation (250 to 650 ft.), but on the opposite side they reach nearly 3000 ft. "Craters are first found at some distance, and but few in the mountains themselves, though those very obvious;" a great contrast, by the way, to the aspect of many other large cavities and their rings, as though the eruptive action had here more completely exhausted itself at one wide and unimpeded aperture. One is a small twin-crater (Copernicus A) on the S. slope, already seen by Schr., the larger orifice lying N., so deep that it holds its shadow longer than the great crater itself; its ring, of 6° light, is much more distinct from its interior of 3° than is usual in such little cavities; the small crater B, equidistant from the grand ring S.E., appears of similar depth. Towards the foot of the N.E. glacis, a larger opening, Gay Lussac, has broken through; this with its smaller

*Memoirs Roy. Astron. Society, XXXII. pl. viii.

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