external form, the description of the integument is entered upon, and it is pointed out that if we look upon the tegumentary layer of the Trematodes as having the same structure as that ordinarily described as obtaining in the Cestoda, we must regard the parenchymatous-like cellular layer which succeeds the muscular as being of an epithelial nature, for its fine processes pass out between the muscular fibres, fuse above it, and secrete the "cuticle"; if this view of the nature of the parts be the correct one, it is clear that all that has been said about the presence of nuclei in the cuticle must rest on erroneous observations.

The movement of the body of Gasterostomum is described as being effected in the following fashion: the body is narrowed and elongated by the contraction of the circular muscles, the head is then protruded, the sucker widens and deepens, and at the same time the muscles in the upper lip of the sucker, aided by others, bring about a flattening of the anterior surface of the body and the formation of a dorsal ridge by the aid of which the body fixes itself; by the contraction of the longitudinal muscles the body is drawn after the sucker.

In both Bucephalus and Gasterostomum it was impossible to detect the limits of the cells of the parenchyma, but in the latter they were clearly seen to be of two forms; some elongated or branched, which were of a connective or muscular nature, and others rounded and less coloured, which seemed to take a part in the osmotic distribution of the nutrient material. The nervous system is briefly described.

In Bucephalus we find at the last third of the body a small tubular depression of the integument, which leads into the pharynx; this can suck in fluid by enlarging and then undergoing a peristaltic contraction. The oesophagus is formed by a homogeneous layer. In the intestine there are large yellowish cells; if the animal has been for a long time in water the intestine is found to have fluid contents in which float greenish yellow spherical concretions. The intestine may seem to be produced into two processes, which appear to owe their origin to the compression, on the ventral wall of the body, of the ventral sucker.

The arrangement of the muscles of the pharynx is the same in Bucephalus as in Gasterostomum; in the latter the stomach has an oval contour, while the intestine has in form, position, and structure a considerable resemblance to that of the Rhabdocœlida. The author is the first who has detected the presence of a distinct œsophagus in Gasterostomum.

The quantity of water which passes through the water-vascular system of Bucephalus is so great that it may well be supposed to have a respiratory as well as an excretory function.

In Bucephalus, cells with nuclei which colour intensely, are to be seen in the last fourth of the body; these are probably converted into the penial sheath; somewhat more anteriorly and dorsally there are several groups of closely appressed cells, the nuclei of which are very intensely coloured; these are supposed to be the indifferent rudiments of the reproductory elements. The generative apparatus of Gasterostomum is described, and a hypothetical account of the mode of action of the copulatory organ is given. By the action of the longitudinal Ser. 2.-VOL. IV.

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musculature of the penial sheath a part of the ductus ejaculatorius is evaginated, until at last the cirrus projects from the genital sinus; this is probably approximated to the orifice of the genital canal. Self-impregnation through the uterus would appear to be possible.

After an account of the remarkable "tail" of Bucephalus, the author passes to the life-history of the two forms. The embryo which, by unknown means, reaches the Anodonta or Unio, becomes there several centimetres long, and gives off lateral branches; the body-wall is thin, and comparable to the parenchyma of the body; within are found Bucephali of various stages of development, and arranged in groups. The Bucephali escape from the mussel by the anal siphon. After swimming about for some hours, the cercariæ sink to the bottom, and, to undergo further development, they must now enter a suitable host; in the neighbourhood of Strassburg this is ordinarily Leuciscus erythrophthalmus (the Rudd); the cysts lie in the connective tissue under the skin, and the containing capsule appears to be very thin and elastic. During the period of encapsulation the animal grows, its water-bladder becomes swollen out and filled with highly refractive spherules, which are probably the final products of metabolism, the stomach becomes relatively smaller, and the anterior sucker and generative organs are developed; the spines become larger and more distinct. If the host fish is eaten by another fish the encysted animals are set free and become sexually mature in the intestine of their new host; but experiments are still wanting to complete this part of the life-history of these parasites.

Development of Dendrocœlum lacteum.-J. Jijima finds this Planarian to be sexually mature once only during its life; the ova contain an immense quantity of yolk-cells, and 24 to 42 embryos are to be found in one cocoon, whereas Metschnikoff only found 4 to 6 in Planaria polychroa. The ova appear to remain for a month or six weeks in their cocoon; this much longer period, as compared with the ten days of P. polychroa, is thought to be due as much to differences in temperature as to those of species. The segmentation is total; the solid morula has a peripheral layer of cells which seemed to be fused together, and an internal mass in which the form of the blastomeres is still recognizable; as these latter multiply the bounding layer increases in thickness, while the free nuclei become more abundant; in fact, there appears to be a process of proliferation. When the embryo is 0.2 mm. in diameter the ectoderm may be seen to be formed by a certain number of flattened cells, and the yolk-cells are then separated from the embryo. The author agrees generally with Metschnikoff in his account of the formation of the pharynx. From the fifteenth to the eighteenth day the yolk-cells inclosed in the cocoon are absorbed by the embryo, which may now be one millimetre in diameter; the pharynx undergoes degeneration and its place is taken by the cavity of the proboscis; a short time before it leaves the cocoon an oral orifice is developed. Like Metschnikoff, Jijima

* Zool. Anzeig., vi. (1883) pp. 605–10. Also Bull. Sci. Dép. Nord, vi. (1883) pp. 100-5.

could not satisfy himself as to the ectodermal origin of the nervous system. The enteric epithelium is formed of cells which are filled with a finely granular protoplasm, or small masses of fat-drops. These appear to owe their origin to the breaking-up of the yolk-cells, and it is in this region only that the cells have fatty contents. The author cannot agree with his predecessor in thinking that the yolkcells are transformed into the epithelial cells of the intestine; he finds, rather, that these yolk-cells lose their individuality and become transformed into irregular masses, while no trace is left of their nuclei.

Rotatoria of Giessen.*-K. Eckstein commences with a review of the genera and an account of the fifty species of Rotatoria found in the neighbourhood of Giessen.

Treating of Floscularia appendiculata he discusses the question whether the long cilia are stiff and immobile, or whether they form currents which carry the food to the mouth, as in other Rotifers. Although never able to observe that the cilia act as described by Ehrenberg, he has been able to convince himself that they are capable of voluntary movements and react to external stimuli. The long, thin, finger-like process which lies among them has probably a sensory function. No distinct ganglion could be detected, but sensory organs were obviously represented by a process on the dorsal surface, lying just behind the wheel-organ, which carried a tuft of setæ. Two red eye-spots were seen at the margin of the orifice, when the animal was in a contracted condition. In the young the wheel-organ consists of a circlet of not very long cilia placed on the edge of the oral funnel. In Ptygura melicerta the foot is provided with large glands, by the secretion of which the animal is able to attach itself to water-plants; its blood-corpuscles are of a comparatively large size. Philodina roseola is to be distinguished from P. citrina by the regular distribution of its coloration, which is not absent from the first and last joints as in the other. In most of his specimens of Rotifer vulgaris Eckstein was able to recognize a lens in the eye; in many cases he found that one or both eyes were divided into two or three, or even into ten or twelve, red corpuscles. In addition to the cephalic ganglion there were detected a large spindle-shaped cell, lying on either side of the rectum, and exactly comparable to the nerve-cells found by Leydig in Lacinularia socialis. In Notommata aurita the ganglion consists of two layers, of which the inner is homogeneous and the outer granular. The mode of locomotion of N. lacinulata is described, as are the voracious habits of Eosphora lacinulata, the differential characters of which, as compared with Triophthalmus dorsalis are pointed out, and it is shown that the latter is not the young of the former. The tail of Scaridium longicaudatum is of great assistance in the execution of rapid movements. Diurella rattulus swims about with its dorsal surface downwards and executes with it movements to the right and left, while the head and tail form fixed points.

In Monostyla lunaris fixed points are obtained by the better deve

*Zeitschr. f. Wiss. Zool., xxxix. (1883) pp. 343-443 (6 pls.).

lopment of the carapace in certain regions. A new genus Distyla is defined as having the carapace depressed, open anteriorly and closed behind; the foot is one-jointed and has two long "toes." The carapace is ridged in the region of the foot, the wheel-organ is feebly developed. D. gissensis and D. ludwigii are the new species.

In Euchlanis dilatata the central organ of the nervous system consists of a number of lobes, and carries one large red eye; it is connected by fine filaments with a pit of tactile function. At the hinder end of the body there are two organs, which appear to be the chief ganglia of the nervous system, for they are long and spindleshaped, and pass anteriorly and posteriorly into fine filaments. Squamella bractea has four eyes, of which the anterior are somewhat larger than the hinder pair, and distinctly contain a refractive body. Behind there is a small tactile tube, which is beset at its end with setæ. In Pterodina the foot has not, as in other Rotifers, the function of an attaching organ, but serves as the hind-gut (?); it can be contracted, but not retracted.

In the second half of this essay Eckstein enters into a general biological, anatomical, and developmental history of the Rotatoria. He finds that there is no true segmentation of the body, and that the jointing of the integument is dependent on the firmness of this layer. The apparent, or rather externally radial form of some (Stephanoceros, Floscularia) is due to their fixed mode of life.

A short comparative account of the wheel-organ is given. The colourless muscles are (1) quite homogeneous, each being formed of a single fine fibre, or (2) have in their centre a chain-of-pearl-like band of clear nuclei, or (3) they are distinctly transversely striated. Whore, as in Scaridium, there is great muscular activity, all the muscles of the body are striated. There appears to be still much to learn with regard to the nervous system, Leydig, for example, refusing to recognize a central organ in Lacinularia, and describing, as chief ganglia, the four nucleated spindle-shaped swellings which lie by the mastax and the rectum. The eye-spots may lie on, behind, or in front of the central ganglion; a convex transparent lens is present in some, though not in all; the eyes may be paired or unpaired, or two may be fused into one. Other red spots, without refractive bodies connected with them, are sometimes found on the wheel-organ. The organ taken by Huxley for an otocyst is rather the calcareous pouch, which is an appendage to the ganglion, and lies either in front of or behind it. It has a spherical or reniform shape, and consists in some cases of irregular aggregations of calcareous granules; it is often continued forwards as a fine granular cord, or as a broad sac-like organ, attached at one end, and by the other projecting freely into the cœlom; further observations are necessary to determine the function of this apparatus.

In all Rotatoria (pace Huxley) the anus lies on the neural side; the excretory system has a contractile vesicle formed of a fine structureless membrane, bounded by a system of delicate and almost invisible muscular fibres, which suddenly contract its lumen; the vesicle enlarges again slowly by the elasticity of its walls, or by the pressure of the inflowing fluid. The canal on either side may be

followed up to the neighbourhood of the wheel-organ; the transverse canal described by Huxley in the cephalic region of Lacinularia has not been detected by any subsequent observer. The author describes the ciliated infundibula as having their thinner end attached to the canal, and their broader one hanging freely into the cœlom. From the upper end a broad cilium projects into the lumen of the funnel, and moves either rapidly or slowly; Eckstein does not think that the swellings are funnels-that is, he does not regard them as open at their free end, but as being completely closed by a hemispherical operculum, to the middle of which the long cilium is attached. Below this operculum there is an orifice, which in the smaller species is small and round, but is generally large and oval; at this hole there commences a very short tube, which leads at once into the lateral canal. By the action of the cilium the waste products of the body are forced into this canal, and so make their way by the contractile vesicle to the exterior. The differences from this typical arrangement which are found in various Rotifers are pointed out, and the resemblances to what Fraipont has found in the excretory organs of the Trematoda are indicated.

The club-shaped pedal organs are next considered, and the tendon by which they are kept in place alluded to; these organs are glands with finely granular contents, and in their middle a line of greater transparency may often be detected, which is probably the optical expression of a groove, in which the secretion of the glands is collected, and by which it is conveyed to the exterior. Sometimes the secretion appears to serve as a means by which the foot may be glued down, in other cases it gives rise to a fine filament; the function, however, of this secretion is not so much to fix the animal down for a time as to attach it until the third joint of the foot is firmly affixed, when the first and second joints being retracted, a vacuum is formed. Respiration appears to be effected through the skin, and this appears to be the function of the pores of Brachionus plicatilis. There is no circulatory system developed. The author is unable to explain the office of the "renal organs" discovered by Leydig in the young of Floscularia, Stephanoceros, &c. (Cohn has already objected to Leydig's view of the renal function of the organ in question); nor can he say anything as to the organ found near the intestine in Squamella, or the body which lies dorsally to the intestine, with which it is connected, in all species of the genus.

Eckstein next discusses the well-known phenomena of the dimorphism of the sexes, and the structure and characters of the reproductive organs; in the Philodineidæ the ovum passes through the earlier stages of development in the uterus, but, owing to the movements of the body, this apparently useful arrangement is of no advantage to the student. Like some later observers, the author would call the winter ova lasting ova, as they are by no means developed in the winter season only, but are rendered safer by the possession of a firm shell. As in other divisions of the animal kingdom, parasitic habit has its effect on the organization of the parasitic form, such as Seison, or Albertia.