apparently no relations to the byssus, it is still more different from the second valve of a Lamellibranch shell. Anatomy of the Stylommatophora.*-A. Nalepa has been chiefly engaged with Zonites algirus, but has also investigated Limax cinereoniger, and Helix pomatia. The large mucous glands which are so often enormously developed in the integument of land pulmonates are proportionately only feebly developed in, and are indeed absent from parts of the skin of Zonites. Transverse sections of the edge of the mantle of Helix show conclusively that the tunica propria of the mucous glands is continued between the epithelial cells. Zonites has no winter operculum, and the absence of this may explain the rare presence of calcareous glands. The author thinks that Simroth's criticism of the supposed olfactory function of the foot-gland is justified by its structure, for maceration shows that it is an agglomeration of unicellular glands. As to the nervous system of the foot, it is to be noted that there are not two primary trunks, inasmuch as the diameter of what have been so regarded is often surpassed by that of their lateral branches. The different reports that have been made on the distribution of a ciliated epithelium in the enteric canal, are partly, at any rate, to be explained by such facts as that the whole stomach is ciliated in very young Helices, while, in the adult, wide tracts are devoid of cilia. The salivary glands of Helix are loose, but in Limax and Zonites compact masses, which in the former lie like a saddle on the short cesophagus, and in the latter form a pretty broad closed ring; they are made up of a number of unicellular glands, and each cell is surrounded by a membrane of connective tissue, which, at its side, is continued into a narrow and generally very long efferent duct. The cells have either finely granular or hyaline contents, and have a different reaction with osmic acid. Each salivary gland receives a strong nerve from the buccal ganglion, and there is a general distribution of the large ganglionic cells, which are characteristic of the sympathetic system. The arteries are continued into capillaries with definite walls, lined by a distinct endothelium, but the veins are more lacunar in character, and endothelial cells are absent from their walls. The characters of the circulatory system are described in detail, and attention directed to the discussion as to the closed or lacunar condition of the vascular system of Molluscs. It is believed that the differences in the results obtained depend not only on the imperfection of certain methods of investigation, but also on the vagueness of the ideas of some as to what is meant by a lacuna and a sinus. Although the arteries end in vessels which are comparable to the capillaries of vertebrates, they do not enter into a continuous connection with venous vessels of similar histological constitution; are the continuations lacunæ (or sinuses), or are they modified capillaries? If by "lacunæ" we mean spaces which, in a histological sense, have no wall, then there are lacunæ; but if by the expression we mean to *SB. K. Akad. Wiss. Wien, lxxxvii. (1883) pp. 237-301 (3 pls.). speak of wide-branched cavities in the tissues, the walls of which are merely formed by connective substance, and which have been individualized and made independent of the tissues of the organs, then there are not here lacunæ. In addition to the contractions of the heart, the author has observed rhythmical contractions in the pulmonary vein and its branches. The ventricle is expressly stated to be innervated from a nerve-plexus, which supplies also the aorta, while the auricle appears to be innervated by a pulmonary nerve; after great trouble Nalepa was able to demonstrate nerves in the musculature of the auricle. After some account of the lung, attention is directed to the kidney, and it is shown that Meckel was in error in supposing that there was a true cameration of the organ, and that the chambers communicated by lateral orifices with the ureter; it seems rather that folds project from its upper and lower walls, but that there is a common central cavity, which, at the tip of the kidney, communicates with the ureter. The lamellæ are ordinarily largely connected by transverse folds, and the spaces thus formed are lined by a secretory epithelium; the uric acid excreted appears to be partly free and partly united with other bodies to form guanin. The penis of Zonites and Limax is distinguished from that of Helix by the absence of a flagellum; and there are certain differences in the vascular supply. The papillæ of stimulation found in the penis of Zoonites consist largely of cells of connective substance, imbedded in intercellular substance, and bounded by the epithelium of the inner surface of the penis. The organ is richly supplied with nerves, as may be well seen in chloride of gold preparations of Limax; the ganglionic cells are arranged in groups, are rounded, and have very large nuclei. A glandular mass in the wall of the vagina of Zonites corresponds to the digitated mucous glands of the Helicidæ ; it consists of tubular follicles which open separately into the vagina, and are lined by a high glandular epithelium. With these the follicles of the bursa copulatoria agree in structure and form. Segmental Organs and Podocyst of Embryonic Limacinæ.*S. Jourdain finds that at the time of the formation of the stomodæal invagination, there appears on either side a labio-tentacular thickening, placed in front of the pallial plate. There is a prepallial swelling formed of a central nucleus of granular matter, which the author regards as true post-embryonic yolk-material, destined to make up for the insufficient quantity of primitive yolk. The segmental organ is paired, and is siphonate in shape, the convexity being superior or dorsal; it consists of a membrane lined by polygonal cells with a large granular nucleus, and with very fine cilia; the external orifice is funnel-shaped. It has no relation to the permanent kidney, which is developed independently. The fate of the segmental organ, no vestiges of which are to be found in the adult, has not been determined. The term "podocyst" is applied to the contractile appendage of the hinder part of the mouth, which is either short, as in Limax agrestis, or elongated * Comptes Rendus, xcviii. (1884) pp. 308-10. and spiral, as in Arion rufus. Its walls are formed by a layer of mesodermal cells with a large nucleus, surrounded by a contractile irregularly stellate protoplasm, the branching processes of which unite with one another. Externally to this layer is a finely ciliated ectoderm; the contained cavity, which exhibits diastole and systole, communicates with the body-cavity, and receives from it and returns to it fluid. Shortly before the young slug leaves the egg the podocyst is completely absorbed. In considering the function of this embryonic organ, we have to note that it is in direct contact with the inner surface of the shell, so that it occupies a very favourable position for the exchange of the necessary gases between the blood and the surrounding air; on the other hand, it is in direct relation to the reserve of material which is used up by the embryo. From a physiological point of view, then, it seems to be comparable to the allantois of the higher Vertebrata. There does not appear to be any good reason for thinking that the prepallial swelling is a contractile sac, which acts antagonistically to the podocyst; all the mesodermal tissues alike distend when the podocyst contracts, and it is only in consequence of the looser texture of the swelling that its movements of dilatation and contraction are more marked and more easily visible. Spicula Amoris of British Helices.*-C. Ashford contributes a comprehensive paper on the "darts" found in connection with the reproductive apparatus in certain Helices. The dart is contained in a short ventricose pouch opening into the lower part of the vaginal tube, a little above the common vestibule, on the right side of the neck. There is usually one: if two are present, the second sac is on the opposite side of the tube from the first. The sac may be simple or bilobate. At the bottom of the cavity of the sac is a conical papilla, which serves as a basis for the dart, which is attached to it by its posterior end. The apparatus is a development of adult life, and especially of pairing time, but this is indifferently present or wanting in species otherwise closely allied. The dart itself is a tubular shaft, of carbonate of lime, tapering to a solid, transparent, sharp point, enlarging at or towards the base, where it assumes the form of a subconical cup. The sides of the shaft are sometimes furnished with blade-like longitudinal buttresses, which serve to strengthen it. They are rapidly formed, may be secreted in six days, and differ in form in different species. They are supposed to serve the purpose of inducing, by puncture, the excitement preparatory to pairing. They are too fragile to do more than prick the tough skin of these molluscs, but sometimes penetrate the apertures of the body, and are found within. A new weapon is formed after It is best extracted for study by boiling the the loss of the old one. sac in caustic potash. Anatomy of Pelta and Tylodina.†-A. Vayssière gives an account of these small and incompletely known molluscs. The presence of "Journ. of Conch., July 1883. Cf. Science, ii. (1883) p. 803. a gill on the right side of the body of Pelta, though difficult to demonstrate, proves that that animal is related to the Pleurobranchiata; other characters of its organization justify us in establishing for it a distinct family. Around the buccal depression there open a large number of mucous glands, not, as in some allied forms, consisting merely of a simple vesicle, but giving rise to mulberry-like masses of racemose character. Each of these masses or aggregates is provided with an excretory duct of some length, and they sometimes not only surround but enter to some extent into adhesion with the nervous centres. The radular apparatus within the buccal bulb does not agree in structure with that of the true Pleurobranchs, and another point of disagreement with them is to be found in the characters of the stomach, which call to mind the arrangements which obtain in the Bullidae; there are in it four large horny plates, the walls are very muscular, and the whole seems to have the function of a gizzard. The gill of Pelta is not well developed, and possesses only three or four respiratory lamellæ; it is connected with the heart by means of the branchial vein; while the heart and its two aortæ could be made out, the remainder of the circulatory system baffled the investigator. The same remark applies also to part of the reproductive system, but it is of interest to note that the author was able to make some observations on a subject which is just now attracting so much attention the development of the spermatozoa. He finds that the male vesicles present the appearance of a cell with a nucleus, in which one may distinguish several hyaline granulations; at the periphery of the male cells there are a certain number of granulations, similar to those of the nucleus. This observation leads to the supposition that here, as in Helix (Duval), there is an endogenous formation of nuclei. Free from these mother-cells we see a large number of "polyblasts more or less developed; in one in an advanced stage, each bud or "spermatoblast" is seen to be only connected with the primitive cell by a delicate peduncle which, later on, forms the anterior part of the spermatozoon. The spermatoblasts continue to elongate, until at last we have a large number of spermatozoa which are attached by their heads. The oesophageal nerve-collar is formed by three pairs of ganglia which are connected with one another by short commissures; of these the cerebroid ganglia are of a pale orange colour, while the pedal and the visceral are more deeply orange. Tentacles being absent, it is possible that olfactory organs are present, but the author was not able to convince himself of this; the eye has the ordinary Opisthobranch structure, while the otocysts are of some size, one only being present in each auditory cell. The author's investigations lead him to concur in the suggestion of J. E. Gray, that the family Peltida should be instituted for the reception of this form. Tylodina is next dealt with, and its relations to Umbrella are particularly insisted on; differences in the number and form of the teeth of the radula were observed to obtain with age; the stomach is provided with a chitinous triturating apparatus; the commissures connecting the nerve-centres are excessively short, and the cerebroid ganglia are proportionately large, owing possibly to the complete absence of visceral ganglia. Absolute Force of the Adductor Muscles of Lamellibranchs.* F. Plateau has commenced a series of researches on the absolute force of the muscles of invertebrates by an investigation on certain Lamellibranchs. The name of absolute or static force was given by Weber to the force measured by the weight which exactly equilibrates the contraction of a muscle; in other words, if a muscle is fixed by one end, and a weight suspended at the other, the absolute force is measured by the maximum weight which the muscle in action can carry without either elongating or contracting. Hitherto observations seem to have been confined to the frog and to man. After a notice of the work of preceding investigators into the physiology of Lamellibranch muscles, the author points out that in most of this group the adductor muscles may be found to consist of a transparent (generally the largest) and an opaque portion; the latter appears to be formed of smooth, the former of transversely striated fibres. The experiments of Coutance show that in Pectens the two muscular portions have different functions: while the transparent muscle contracts rapidly, the opaque smooth muscle does so slowly. Plateau has experimented on twenty different species, but finally limited his researches to Unio pictorum, Cyclas rivicola, Artemis exoleta, Tellina incarnata, and Pandora rostrata. A full account of the modes of experiment is given, together with elaborate tables of the results; these cannot be reproduced here, and it must suffice to say that it has been found that the only way of usefully comparing the muscular force of Lamellibranchs with that of the higher animals is to discover the absolute force of the muscles for each square centimetre of transverse section. When the comparison is thus made it is found that the absolute force of the adductors of Lamellibranchs is analogous to that of vertebrates. To the objection that molluscan muscles are smooth, and that vertebrate muscles are transversely striated, the only possible answer at this moment is that the author has also made some investigations on the muscular force of Crustacea, which will shortly be published and in which he hopes to explain the apparent anomaly. Water-pores of the Lamellibranch Foot.-H. Griesbach has maintained the existence of pori aquiferi in the Lamellibranch foot, while J. Carrière held the contrary view. J. T. Cattie § has studied a considerable number of species, and does not find the least trace of aquiferous pore; and T. Barrois || arrives at the same results. He discusses the work of Carrière and himself, and finds that they have studied most of the forms where the presence of aquiferous pores has * Bull. Acad. R. Sci. Belg., vi. (1883) pp. 226–59 (1 pl.). + See this Journal, iii. (1883) p. 353. Ibid., p. 639. § Zool. Anzeig., vi. (1883) pp. 560-2. "Private imprint from Lille, dated October 30th, 1883." Cf. Science, iii. (1884) pp. 130-1. |