the character of the latter, and the method of its construction. In its earliest stages it is a transparent, smooth, and homogeneous slimelike excretion, within which the worm may be very clearly seen, as it works its way forward or drags itself backward by means of its pedal hooks and spines. Later on, the anterior extremity thickens and becomes more and more opaque, and, as Dr. Leidy has observed, "feebly annulated," presumably from the adherence of effete particles, and their compression by the repeated withdrawal of the ciliated tentacles into the mouth of the tube. This method of prolongation must continue during the residence of the worm, and in consequence, if supported, it may sometimes reach a length which is several times that of its inhabitant. Miss S. G. Foulke has also examined * the worm and describes the pulsation of the green tentacles. To ascertain how long the cilia upon the tentacles would continue their motion after separation from the body of the worm, both lophophores of an adult were cut off above their junction. At first the tentacles remained closed from the shock, but soon they were expanded, the cilia displaying active motion, and presently the two separated lophophores began to move about in the zoophyte trough. This motion was produced by the action of the tentacles, which bent in all directions, the tips touching the glass, and was not a result of the currents produced by the cilia. In a few minutes one lophophore had crawled in this manner quite across the trough, while the other remained floating in the water near its first position. In the case of this latter the motion was produced by the ciliary currents, and was entirely distinct from the crawling above noted. During this time the decapitated worm had sunk to the bottom, and, though turning and twisting a good deal, did not attempt to protrude the mutilated support of the lophophores. Its body was so much contracted that the segments were not above one-third their usual size. At the end of five hours the worm was apparently dead, numbers of infusoria had collected to prey upon it, and the surface of the body presented a roughened appearance as though covered with tubercles. The lophophores were still crawling and swimming about. At the end of the eighth hour the lophophores had ceased to crawl, but the ciliary action, though feeble and uncertain, still continued. The body of the worm was then covered with a thick fungoid growth, consisting of transparent rod-like filaments 3/16 in. in length; some of the filaments presented a beaded appearance. All motion of the cilia upon the tentacles had ceased, and these also were being devoured by infusoria. Life-History of Thalassema.t-H. W. Conn describes (in a prcliminary paper) the early stages of development of Thalassema mellita that inhabits empty "sand-dollar shells." Its anatomy is much the same as that of Echiurus described by Sprengel. It is dioecious. The ova and mother-cells of spermatozoa are simply modified cells of the peritoneal lining of the body-cavity, in which, whilst developing, they * Proc. Acad. Nat. Sci. Philad., 1884, pp. 48-49. + Stud. Biol. Lab. Johns Hopkins Univ., iii. (1884) pp. 29-35 (1 pl.). float freely, being driven, when mature, into two sexual pouches at the anterior end of the body. In about fifteen minutes after fertilization two polar globules are protruded from the egg, exhibiting a rhythm precisely similar to that of the segmenting ova. Segmentation is, exceptionally among Annelids, perfectly regular and uniform. About the 6th hour a gastrula is formed by a typical invagination, and at the same time the region opposite the blastopore becomes marked off as the anterior extremity and already functions as a head. A preoral band of cilia appears and is subsequently replaced by a row of longer and more powerful cilia. The transformation of the gastrula into a trochosphere larva takes place by a peculiar method of growth whereby the direction of the long axis is changed. The mesoderm has a dual origin resulting in two different systems. First there is formed the two mesodermal bands so common to Annelid larvæ, and the second part of the mesoderm consists of a large number of unicellular muscles that separate from the endoderm at the time of the invagination, having thus an origin very similar to that of the mesoderm in Echinoderms. Three other ciliated bands soon make their appearance, one immediately behind the mouth, a second just in front of the anus, and a third is found upon the ventral median line in precisely the place where the ventral nerve-chain is to arise. It is thus seen that both the cerebral ganglion and the ventral nerve-chain are preceded by the development of cilia from the very cells from which the nervous elements are to arise, an interesting point as indicating that already these cells are differentiated as elements, although at first there is no trace of any nervous system. The further changes observed were the segmentation of the mesodermal bands and the origination of the ventral nerve-cord from the ectoderm as a bilateral structure. nervous before Spermatogenesis and Fecundation in Ascaris megalocephala.* P. Hallez finds that the spermatospores of Ascaris megalocephala are at first formed of a homogeneous, extremely transparent, and nucleated protoplasm. Increasing in size they give rise by division of the nucleus to four protospermatoblasts which become separate. These similarly produce a second generation of cells-the deutospermatoblasts, and have a central blastophore in young, though not in old, males. When the deutospermatoblasts attain to a size of 6 μ in diameter their protoplasm, which was homogeneous, becomes finely granular. When they have a diameter of about 18 μ they divide into two, and henceforward their protoplasm is filled with refractive granules. Before they pass into the seminal vesicle the spherical cells conjugate by pairs, and the nuclei fuse with one another. Two cells again separate, and at this moment corpuscles like polar globules are to be observed; these, which the author calls waste-corpuscles (corpuscles de rebut) finally entirely disappear. The deutospermatoblasts are then introduced into the organs of * Comptes Rendus, xcviii. (1884) pp. 695-7. the female, and are at this time 18 to 19 μ in diameter, spherical in form, having their protoplasm filled with refractive granules, which call to mind the vitelline granules, and they have a nucleus which is easily stained. In the female organs the refractive or nutrient granules diminish gradually and finally disappear. The deutospermatoblasts now present the most varied forms, and look more like Amabæ. It is at this time they become spermatozoa, the substance of which is formed from the interior of the cells, and appears first as a differentiation of the protoplasm, and surrounded by a delicate granular layer -the remains of the deutospermatoblast; it is remarkable that the deutospermatoblast is constantly outside the spermatozoon. This latter has at first the form of a rounded cylinder, but its surface rapidly becomes spiral and one end enlarges as the other diminishes. At the moment of fecundation the ovum is surrounded by a finely striated zone, to which the conical spermatozoon becomes attached by its base; the yolk contracts slowly, the spermatozoon enters, but there is apparently no micropyle; the peripheral part of the yolk forms a granular zone which surrounds the male element, part of which advances as a fusiform male pronucleus to fuse with the female pronucleus. The yolk again contracts and a polar globule is formed. Structure of Derostoma Benedeni.*-P. Francotte, after an historical review of the characters of the genus Derostoma and its rhabdocœlous allies, gives a short diagnosis of the new species he has discovered at Andenne, where it was found in a stream, in the midst of a number of Tubifex rivulorum on which it feeds. In the anterior part of the body the epithelial cells are higher than elsewhere, their cilia are longer, and between the cells the ends of nerve-fibres could be detected, though their exact relations were not made out. The pharyngeal bulb is largely formed of muscular fibres, and is moved by a set of thick fibres which are attached to its dorsal and ventral surfaces and so produce movement in all directions. The muscular fibres in all parts of the body are smooth and nonnucleated; they appear to be formed of a large number of delicate fibrils. When a specimen has been rendered transparent it is possible to see, in the anterior region, two ganglia united by a transverse commissure; each of these ganglia gives off two nerves which pass to the epithelium, and two others which are longer and pass backwards to innervate the various organs of the body; on the ventral surface of the worm there is yet another pair of nerves. The two ganglia and the commissure are formed externally by ganglionic cells, while the centre is filled with nerve-fibrils; on the course of the nerves large nerve-cells, similar to those of the central nervous system, are not rarely met with. The cells which line the digestive tract are stated to be globular during digestion, and to be elongated in sections made from fasting specimens. The penis is not, as in some species, chitinous, but is formed of muscular fibres. Between the ovary and the receptaculum seminis * Bull. Acad. R. Belg., vi. (1883) pp. 723-35 (1 pl.). there is a cæcal glandular tube, which appears to be a degenerating ootype, which now probably serves as the organ which secretes the fluid which, on hardening, forms the chitinous shell of the egg. In addition to what the author has already discovered in the characters of the excretory system, he is now able to state that the large trunks are formed of flattened clear cells, that the lacunæ are filled with corpuscles, and that there are very delicate canaliculi, without any proper wall, which unite the lacunæ with one another. In opposition to Lang, the author still regards these lacunæ as representing a true cœlom. Hæmoglobin has been detected in the anterior part of the body. Opisthotrema, a New Trematode.*-P. M. Fischer describes a new Trematode, which he calls Opisthotrema cochleare, and which was taken from the tympanic cavity of Halicore dugong; it is remarkable for the characters of its generative organs, and especially for the fact that they open at the hinder end of the body-hence the generic name. These openings are separate from one another, ventral in position, and placed at the base of a circular pit with well-defined margins. The The testes are paired and symmetrical, rounded in form, but more or less distinctly lobed at their periphery; as the production of sper matozoa increases, the lower segment of the testes approaches nearer and nearer to the ventral surface. The testes consist of tubes, often closely packed, and bounded by a homogeneous structureless envelope, which is, apparently, a direct continuation of the cuticle. separate tubes are connected together by a fibrous connective tissue, and are covered by a common envelope which appears to be of the same structure as that of the separate tubes. In young examples, naked, epithelial, finely granulated cells are to be found within the tubes; these, by division, give rise to the cells which, in older forms, are found grouped into rosettes: with these are associated thick cords of compressed mature seminal filaments. Like the testes, the seminal ducts are paired, and have the common testicular investment continued on to them, while the extremely delicate muscular layer is now better developed. As the ducts enter the penial sheath they become united, and their lumen widens out, being here homologous to the so-called vesicula seminalis anterior of other Trematodes; the width of the coiled tubes varies with the maturity of their contents. The penis is so arranged that, on its extension, there is a pressure on its cavity and on the full seminal reservoir, the contents of which are thereby forced into the vagina. The penis has no armature of spines. As in other Trematodes, the unpaired ovary is followed by the yolk-glands and the complex of shell-glands; connected with the oviduct is a receptaculum seminis, which is of very regular ellipsoidal form in young, though not in old individuals. In discussing the mode of fertilization of the Trematoda, the author points out that there may either be self-impregnation or conjugation with another individual. The former may be effected by * Zeitschr. f. Wiss. Zool., xl. (1884) pp. 1-41 (1 pl.). a third vas deferens, or there may be self-copulation, the erected penis being received into the adjoining female duct, or, lastly, the genital cloaca may come into function, its opening to the exterior being closed by muscles, the contraction of which drives the expelled sperm into the vagina. As to the form now under consideration, we know that there is no third vas deferens, and that the penis would have to be extraordinarily bent to be able to enter the adjoining female orifice; while, finally, the absence of a genital cloaca excludes the possibility of self-fertilization by its aid. The author describes the mode by which he supposes two of these hermaphrodite Trematodes may fertilize one another. The system of excretory vessels may be, in Trematodes, ordinarily divisible into three parts; the first of these, the central organ, which is distinguished from the other parts by its muscular investment, was not detected in the new genus. At the hinder pole of the body there are to be seen two well-developed canals, which pass forwards and are, at about the middle of the body, provided with lateral branches, two of which are much longer than the third; from these there again arise fresh lateral branches, which end blindly and never anastomose with one another; these ducts are bounded by a doubly-contoured membrane, which is regarded as being certainly a continuation of the external cuticle. Within this, and, especially, applied to its walls, are granules of some size, and high refractive power. The author was unable to detect the ciliated infundibula described by Fraipont and Pintner. In his account of the nervous system, Fischer directs attention to structures which appear to represent ventrally placed and peripheral ganglionic cells, the presence of which is of especial interest when we know that the ventral body-muscles are particularly well developed in this form. The parenchyma of the body is composed of cells which vary greatly in form and appearance; at the anterior pole of the body they are smaller and rounder than at the hinder end; when largest, they have a striking resemblance to those of plants. The specimens for examination were hardened in absolute alcohol, coloured with picrocarmine or hæmatoxylin, sometimes with an ammoniacal solution of carmine. They were rendered transparent by oil of cloves, and by being set up in Canada balsam and chloroform for permanent preparation, or in glycerine when the sections were not intended to be preserved. Polycladidea.*-A. Lang has published the first half of his monograph on these worms. It will be remembered that the author has divided the Turbellaria (the Nemertinea being excluded) into Polycladidea, Tricladidea, and Rhabdocœlida. He now subdivides the first suborder into two tribes:-I. P. acotylea, where we have the three families of Planocerida, Leptoplanidæ, and Cestoplanidæ ; and II. P. cotylea, including the Anonymidæ, Pseudoceridæ, Eury *Fauna u. Flora des Golfes von Neapel, Monographie xi. (1884) part i., 240 pp. (24 pls.). Ser. 2.-VOL. IV. 2 D |