By the study of the development of Prosobranchs and fresh-water Pulmonates, especially of Paludina vivipara (8), Bythinia tentaculata (9), and Planorbis corneas (10), I was led to adopt Professor Ray Lankester’s (19) view on the homology of the only remaining kidney or nephridium of most Prosobranchs. I found that the kidney of Paludina and Bythinia, which in the adult lies to the left of the anus, was, before the torsion takes place, situated to the right of the anus, and consequently must be homologous to the actual left kidney of Fissurella, Patella, Haliotis, Trochus, &c. Whilst in so-called leiotropic species1 the actual kidney is the left one, it is just the contrary in dexiotropic species, such as Planorbis, where the actual right kidney is, before the torsion, situated to the left of the rectum. I also found in Paludina a rudiment of the actual right kidney lying before the torsion to the left of the rectum, and observed that its duct was converted into that of the genital gland. Comparing this fact with the statement that the right kidney of Zygobranchs and Cyclobranchs serves as a duct for the sexual products, I was led to the conclusion that the actual right kidney disappears or becomes highly modified, while its duct is converted into that of the genital gland.

Reading the works on the comparative anatomy of Gastropods, I was struck by the contradictory statements about the reno-pericardiac duct in Zygobranchs, Cyclobranchs, and Prosobranchs. Ray Lankester, in his first paper on Patella (18), stated that he found a communication between the actual left kidney of Patella and the pericardium. In a second paper he only describes a right reno-pericardiac duct in the same species. V. Jhering (16) could not find any communication between either kidney and the pericardium inFissurella and Patella, at least, as he says, with any certainty, while he was able to find it in Haliotis. Bontan (2) failed to see the left kidney in Fissurella, and could not find a reno-pericardiac canal in the right kidney. B. Haller (13) describes a right reno-pericardiac duct in Fissurella. Wegmann does not mention any communication for either kidney and the pericardium in Patella (28), although he found a left renopericardiac duct in Haliotis (27), where the right kidney has no opening into the pericardium. Cunningham (7), at Ray Lankester’s suggestion, re-examined Patella, and found a reno-pericardiac duct for both kidneys. The last anatomist who studied the kidneys of a great number of Prosobranchs, R. Perrier (23), describes a right reno-pericardiac duct in Fissurella and Patella, but could not find a left one in either of these two species. On the other hand, he found only a left pericardiac duct in Haliotis, Trochus, and Turbo.

The conclusion to be drawn from this historical résumé is, I think, that the subject was well worth a new investigation. I accordingly have studied five different species of Fissurella, Emarginula, Puncturella (closely related to Rimula), one species of Patella, a Tectura, one species of Haliotis, one of Trochus, and a Turbo. My results, as the sequel will show, are somewhat surprising as regards Fissurella and Patella, whilst they only confirm prior investigations as regards Haliotis, Trochas, and Turbo.

I further hope to offer a plausible explanation for the contradictions between my predecessors and myself, and must add that to attain this end I expended more time and trouble than it cost me to arrive at the conclusions which I intend to describe in this paper.

Methods employed in the Present Investigations

In order to fix the tissues as rapidly and as perfectly as possible T made use of the following fluids, viz. Kleinenberg’s fluid (picro-sulphuric) with a few drops of osmic acid, and a mixture of sublimate and glacial acetic.1 The specimens of Patella and Fissurella were dropped living into these fluids, left there for about a quarter of an hour, then thoroughly washed with water, and afterwards hardened in spirit from 40 per cent, up to 90. I tried Flemming’s fluid (chromosmic acetic), but was obliged to discard it, as it made the tissues too brittle. When the specimens have been in spirit some time they can be easily taken out of the shell by pulling them gently with a pair of forceps. They then come out perfectly uninjured.

For Trochus I had to use a different method, as the shell and operculum make the animal impervious to the fixing liquid. The shell in the species which I investigated is so thick and hard that it cannot be removed while the animal is living without injuring it severely. I therefore put the Trochuses into sea water and 1 per cent, absolute alcohol (according to Signor Lo Bianco’s method) in order to draw the anterior half of the body out of the shell. After a day or two the animals are paralysed without being killed. It is then possible to pull the anterior half of the body out of the shell and to plunge them into the fixing liquid, which can then easily penetrate into the shell and the mantle cavity. The specimens were then hardened in spirit for a few days. It is then possible to crack the shell with a hammer and to remove it with a pair of forceps without injuring the specimen in any way.

The rest of my material was not obtained fresh, but had been preserved in spirit. The preservation was satisfactory in nearly all cases.

The stain used was principally alum carmine, which is very valuable for molluscs, and can be used to stain in bulk. In many cases I used hæmatoxylin or methyl green as a plasma stain. They easily penetrate when only a part of a specimen has been prepared for sections.

In most cases I sectionised only the pericardium and the mantle cavity, after having removed the foot and other organs with a razor or a pair of scissors. In this way a great deal of time and trouble may be saved, and the stains penetrate more easily. It is of course necessary to have hardened the specimen thoroughly beforehand. By the same method it is easy to dissect out the pericardium, mantle cavity, and kidneys. Such a preparation can then be mounted whole in balsam, and is most useful for the topography of the different organs.

The sections were cut with Yung’s microtome; the embedding was done in chloroform and paraffin. Besides dissections and sections I also made use of injections, at the special request of Professor Ray Lankester. I myself am strongly prejudiced against this method, as it is very likely to mislead. I used soluble Berlin blue, and injected by blowing the solution through a fine glass pipette with the mouth. Applied in this way the injections method confirmed the results obtained by dissection and sections in every case. When, on the contrary, I used a syringe and a strong pressure, the coloured fluid often broke through the walls of the pericardium and kidney in places which I consider as loci minoris resistentise, and which shall be described in the sequel.

Before beginning my correspondence with Professor Ray Lankester on the points at issue I had always injected from the pericardium, as morphology and physiology show that the liquid which fills the pericardium is expelled by the kidney, and consequently in a centrifugal direction. By request of Professor Ray Lankester, I made some more injections from the kidneys, with the same results, which I have already described. Personally I do not think the latter method of injection a good one. I consider it even less reliable than the first, as a great many animals possess a valve between the pericardium and the reno-pericardiac duct, in order to prevent the excreted liquid from flowing back into the pericardium.

The shells of most of the species of Prosobranchs studied by me in the course of these investigations were determined by Professor Boettger, in Frankfort-on-the-Main, and Dr. Kobelt, in Schwanheim, near Frankfort-on-the-Main. I beg both these gentlemen to accept my thanks for having so readily fulfilled my request.

I propose to begin with Haliotis and Trochus, where a reno-pericardiac canal (left) really exists. I shall afterwards describe the other forms in which no such a structure exists. I adopt this order so as to show that I have not overlooked the communication between pericardium and kidney, which is really quite easily to be found in Haliotis, Trochus, and Turbo, even by dissection alone, whilst in Fissurella and Patella no trace of such a structure could be found.

1. Haliotis tuberculosa

This species has been studied by v. Jhering (16), Wegmann (27), Haller (13), and Perrier (23). I am happy to be able to confirm Jhering’s, Wegmann’s, and Perrier’s statements. Jhering’s figures are certainly a little schematic, as Haller remarks; but whilst Haller’s figures are very good and exact, his interpretation is quite incorrect. He considers the duct of the right kidney exclusively as the genital duct, and describes a communication between the right kidney and the left (Haller’s papillary sack) which really does not exist at all.

Fig. 1, a view of the dorsal surface of Hal. after removal of the shell shows the pericardium (Pc.) in situ at the hinder end of the mucous gland (muc.), and the mantle cavity (Af.). To the left lies the left kidney (Nl.) which is considerably smaller than the right one (Nr.), of which a part can be seen on the right side of the pericardium. All these organs are viewed by transparency through the mantle. In order to display the external openings of the kidneys, it is necessary to lay open the mantle cavity and to turn back the rectum, which is dorsally attached to the mucous gland. A dissection of this kind is figured in fig. 2, where both nipples are to be seen (XI. and Xr.) at the base of either ctenidium (Bl. and Br.), and to either side of the rectum (R). The right ctenidium (Br.) is about a fifth smaller than the left. This fact has already been mentioned elsewhere, but I desire to lay special stress on it, as it will be made use of in the comparative part of this paper.

The right kidney is a large gland, the shape and relations of which have been accurately described by Wegmann (27), while Perrier (23) has ably figured its histological structure. Having no intention of entering into histological detail I simply refer the reader to Perrier’s memoir on this subject.

The left kidney has the shape, and in large specimens the size of a hazel-nut; the numerous papillæ which it contains give it externally a velvety appearance (Wegmann).

When the pericardium has been dissected out, opened transversely from behind and the heart (ventricle and both auricles) removed, the opening of the left reno-pericardiac duct into the pericardium can be easily seen (fig. 3, Y) ; it is situated to the left of the rectum, and lies between this and the left auricle. This is shown in a frontal section (fig. 9). The reno-pericardiac duct is, as Perrier has already stated, a canal of no inconsiderable length, and its presence can be readily detected in frontal sections, while, on account of its direction, it is somewhat more difficult to trace in transverse sections. There is no proper genital duct in Haliotis, and the gonad communicates with the right kidney by a slit-like opening, which, according to Perrier (23), has a special valve closed in all times except in that of sexual maturity.

2. Trochas turbinatus, Born

The topography of the pericardium and kidneys is practically the same in Trochus as in Haliotis; Turbo is so nearly allied to Trochidæ that I think it unnecessary to give a full description of this form. My friend Mr. Macbride and myself have dissected two large specimens of Turbo, and have found that it differs but very slightly from Trochus, and these differences are so small that they may be neglected entirely with regard to the points which form the subject of this memoir.

Haller has made the same erroneous statements about Turbo as about Haliotis, which have already been corrected by Perrier, with whose observations my own agree perfectly.

When the mantle cavity has been opened by a longitudinal section parallel to the attached side of the only remaining left ctenidium (Bl., fig. 4), and viewed from the ventral surface, the rectum (R.) is seen in the shape of a long tube opening into the mantle cavity (M) by the anus (A.), which is situated at abopt the fifth of the total length of the gill from its proximal end. To the left (in reality the right) of the rectum the duct of the right kidney is seen as a long tube opening into the mantle cavity by an orifice (Xr.). To the right (in reality the left) another wider tube is to be seen, which does not run parallel to the rectum as the duct of the left kidney. This tube or sac is the left kidney, which also opens into the mantle cavity by a button-hole-like orifice (AZ.). The left kidney or papillary sac extends back to the pericardium (Pc.), which has been opened in order to show the two auricles of the heart. The axis of this organ is oblique to the longitudinal main axis of the body—a fact which is already apparent in Haliotis, but to a lesser degree.

In a series of transverse sections beginning at the anus, or, better, at the point at which the rectum issues from the pericardium anteriorly, and extending back to the point at which the rectum issues from the pericardium posteriorly, a large sinus (bas., fig. 13) can be discerned lying ventrally to the rectum (R.), and above the mantle cavity (M.). This sinus is morphologically equivalent to the basibranchial sinus existing in Haliotis and in Fissurella-like forms, where we shall meet with it again. Perrier (23) and Bernard (1) have shown that the blood coming from the right kidney, the head, and the epipodium is collected here, and hence is sent to the ctenidium or ctenidia.

The vein (v.) which in Trochus runs into the afferent vein of the ctenidium is seen to the left of the rectum, dorsally from the left kidney (Nl.) or papillary sac. This organ has the closest resemblance to the corresponding one of Haliotis, and shows a great number of the characteristic papillæ.

The right kidney (Nr.) is to be seen on the same section to the right of the basibranchial sinus, The section only shows the part which acts as a reservoir for the urinary secretion, and has been called urine chamber (Urinkammer) by B. Haller (13).

Projecting into the ventral wall of the papillary sac can be seen the transverse section of a duct which lies between the mantle cavity and the papillary sac or left kidney. In fig. 3 (Y.) it is seen to open into the left kidney ; two or three sections further back this communication is entirely obliterated (C, fig. 8). Proceeding still further backwards, the duct in question can again be seen to open into a space lying ventrally to the basibranchial sinus (fig. 12), and which, as another section still further back clearly shows, is a ventral and anterior prolongation of the pericardium (Pc.). In fig. 12 two distinct portions of this cavity may be seen (Pc. and Pc.), the one already described and opening into the reno-pericardiac duct (y.), the other separated from the first by the basibranchial sinus (bas.) lying immediately below the rectum, which is already enveloped by the ventricle (V.). Fig. 7 shows that further backwards the two portions unite (Pc.), and that now. the basibranchial sinus (bas.) is divided by the pericardium into two separate halves.

By comparing the transverse series with horizontal ones in which the reno-pericardiac duct can be readily found, and with dissections, it can be clearly seen that the portion of the pericardium leading into the reno-pericardiac duct is a longish prolongation extending ventrally and anteriorly to the heart. Its position corresponds to that of the reno-pericardiac duct already described in Haliotis.

The right kidney, the properly secreting part of which is to be seen in fig. 12 (Nr.) below the urine chamber, does not communicate either with the pericardium or with the left kidney or papillary sac. There is a very short true genital duct in Trochus and Turbo. The gonad which lies quite close to the right kidney discharges its products into the mantle cavity, as v. Jhering has already stated.

3. Fissurella, Emarginula, Puncturella.1

These species, differing exceedingly slightly in the general appearance, position, and histological texture of both kidneys, can be all described at a time.

I examined five different species of Fissurella, viz. the four different species which are to be found in the Gulf of Naples, that is to say, Fissurella costaria, Bast. (= mediterranea = europæa), Fiss. græca, Linné, Fiss. nubecula, L., and Fiss. gibberula, Lamarck. I also dissected a Chilian species, which I believe-to be the Fiss. maxima.

I think that a few hints concerning the determination of the four species found at Naples may prove useful, as I found considerable difficulty in determining them with the diagnoses given by conchologists.

Fiss. costaria, also called reticulata, is the largest species, and can attain a length of 4 to 5 cm. ; the shell, which anteriorly is narrower than posteriorly, is provided with about twenty well-marked ribs diverging from the fissure ; between these ribs there are several others less well defined. Fiss. græca is generally about half the size of the species which I have just described, the shell is just as broad in front as behind, the ribs are all about the same size, and formed by a succession of scale-like processes of the shell, which make it much rougher than that of F. costaria. Fiss. gibberula is mostly about a third smaller than F. græca, and can be easily recognised, as the part of the shell situated behind the fissure is higher than that situated before the slit. The shell has, therefore, a hunchbacked shape, whence the Latin name. The shell of F. gibberula is nearly quite smooth.

If the shell of the three species I have just described be placed with the aperture downwards, the slit upwards, on a table, it can be readily noticed that the shell only touches the table at its anterior and posterior end. If, on the contrary, the same experiment is made with the shell ofF. nubecula it will be seen that the rim of the shell touches the table in every point of its circumference. F. nubecula is the smallest of the Neapolitan species, being generally smaller than F. gibberula; occasionally,however, very large specimens get nearly as big as those of F. græca. The shell of F. nubecula is much flatter than those of the three other species.

I could state a great many other minor points by which the four species I have just described might be distinguished, but I think that those I have mentioned will suffice, as they afford a good and convenient criterion. The Emarginula I examined also belongs to the fauna of the Gulf of Naples, but is difficult to obtain. Dr. Kobelt, in Schwanheim, near Frankfort-on-the-Main, who had the kindness to determine a part of my material, labelled it Emarginula Huzardi, Pay. This species is rather scarce here, and I worked on specimens which had been preserved in strong spirit by Dr. Schiemenz, who kindly placed several of them at my disposal. The preservation was quite satisfactory.

The Puncturella, which like Fiss. maxima is a Chilian form, was collected by Chierchia in November, 1882, and was less satisfactorily preserved, the gills and epithelium of the mantle cavity being somewhat macerated. Fortunately the preservation of the kidneys was good.

B. Haller (13) having given a very fine figure of the shape and position of the right kidney of Fissurella costaria I thought it superfluous to give another. When the shell has been removed the right kidney is seen surrounding the pericardium on the right side. It sends a prolongation to the right, which extends further forwards than the pericardium itself, and another one to the left, so that the pericardium is entirely surrounded by the right renal organ, which extends far back nearly to the posterior end of the animal. In order to see the left kidney it is necessary to remove the mantle funnel which projects through the slit of the shell (fig. 22, Fi.), with the underlying sinuses of the funnel, also to open the pericardium dorsally and to lift up the left auricle. It is better to remove the heart entirely by cutting the rectum anteriorly and posteriorly to the ventricle, the two auricles at the origin of the branchial efferent veins, and the aorta (ao.), which issues from the ventricle posteriorly, ventrally, and on the left.

Such a dissection is to be seen in fig. 5. The bottom of the pericardial cavity is displayed (Pc.) ; on the right a part of the right kidney (Nr.) is seen by transparency through the ventral wall of the pericardium. R. and R. are the two cut ends of the rectum on its way through the pericardium ; ao. is a section of the aorta, which has just left the heart and pierces the ventral wall of the pericardium. The left kidney (Nl.) is exceedingly small compared with the huge right renal organ. It lies embedded in the anterior wall of the pericardium, between this and the basibranchial sinus. It generally has the shape of a sac (fig. 19) provided with a bent duct leading into the terminal papilla. Sometimes, however, as in fig. 5, it is slightly ramified.

In order to see the anterior openings of both kidneys and their nipples or papillae it is best to make a transverse section of the mantle cavity just in front of the anus. This I did on a well-hardened specimen, first making a horizontal section with a sharp razor, passing just below the bottom of the mantle cavity, then a transverse one just in front of the anus.

Fig. 6 shows a preparation obtained by this method. The mantle cavity is seen to be divided into four portions or nooks by the branchial supports (br.) on either side. One may, therefore, distinguish an upper and a lower nook of the mantle cavity on either side (Msr., Msl., Mir., Mil.). The anus lies at the end of a well-defined papilla which occupies the centre of the cross which divides the mantle cavity in the way which has just been described. On the ventral side of the anus, just above the floor of the mantle cavity (Ma.), a projecting ridge parallel to the mantle cavity may be seen. This ridge is formed by the basibranchial sinus (bas.). The ridge itself bears the two papillae on which the external apertures of the two kidneys lie. The papilla of the left kidney (Pr.) is larger, has a slit-like opening (Xr.), and is situated anteriorly on the right edge of the basibranchial ridge. The papilla of the left kidney (Pl.) is much smaller, and lies further back in the left inferior nook of the mantle cavity. Its aperture is nearly round, and in most cases very difficult to find in dissections. In the preparation just described, the ctenidia which are cut transversely display perfectly the double feathered condition characteristic for the forms with two equally developed gills. The relations of the ctenidia to the auricles (aur.), the ventricle, the nipples of the anus, and the kidneys are shown in fig. 10, which is drawn from Fiss. maxima, in which the pericardium and mantle cavity have been opened ventrally.

At the base of the papilla of the right kidney (Pr.), between this and the pericardium, that is to say, in the hinder wall of the basibranchial sinus, two openings can be seen. The one lying towards the middle line, distinguished by a brownish colour, is the beginning of the left kidney running into its papilla (Xr.); while the other one, lying outside of the first, is the genital duct (Gd.). Both kidney and genital duct have been cut through transversely in the course of the dissection. The same thing magnified ten times is shown in fig. 18. A bristle has been introduced into the genital duct, and is seen to issue out of the sectionised right kidney—a proof that the genital duct opens into the papilla of the right kidney. The left kidney can be easily detected in Fiss. reticulata, maxima, gibberula, and græca; it is a remarkable fact that it has entirely atrophied in Fiss. nubecula, where even the papilla has disappeared.

Fig. 23 shows a transverse section through the pericardium and both kidneys of Fiss. græca. Dorsally and in the middle line the cavity of the pericardium (Pc.) can be easily seen. In it lies the ventricle (V.) surrounding the rectum (R.), to the right of which an artery is seen in transverse section. The section is not absolutely transverse, so that only one auricle, the left one (aul.), is to be seen. Fig. 10 had shown that both auricles are of the same size, and situated symmetrically on either side of the ventricle and the longitudinal body axis. On the ventral side of the pericardium lies the basibranchial sinus (bas.) ; to its right lies the beginning of the right kidney (Nr.), with the commencement of the genital duct (Gd.) situated to the right of the latter. Fig. 26, a part of a transverse section through Fissurella nubecula, shows the genital duct (Gd.), containing young ova, opening into the beginning of the right kidney (Nr.), which also contains some ova. This shows that the sexual products are really discharged through the right nephridium. To the left of the basibranchial sinus (bas.) is the left nephridium (Nl.). The figure shows the tremendous difference in the size of the nephridia. The section of the left is the largest one in the whole series, and still it is surprisingly small, compared to the right kidney, which extends from one side to the other of the section, and insinuates itself between the different viscera (Nr., Nr.). Fig. 21 is a transverse section through the papilla of the right kidney in Fiss. gibberula, showing the external opening of the right kidney (Nr.), situated between the genital duct (Gd.) and the beginning of the right kidney cavity (Nr.).

Von Jhering, Haller, and Perrier are unanimous in saying that the left kidney does not open into the pericardium. Whilst Jhering and Boutan failed to detect a reno-pericardiac duct in the right kidney, Haller and Perrier have described a right reno-pericardiac canal.

I have carefully studied a great number of transverse and frontal series through Emarginula and Puncturella, and the four Neapolitan species of Fissurella, and have absolutely satisfied myself that no such thing exists. The specimens of Fissurella had been most carefully preserved and stained, the sections extended without a break through the whole length of the pericardium. Fig. 16 shows the point in which the right kidney runs into the nipple immediately on the ventral and right side of the pericardium. In this section, as in all others, the brown epithelium of the right kidney is seen to extend over the whole inner surface of the nephridium, without any interruption whatever.

Perrier, in his answer to a letter which I wrote to him on the subject, stated that he had made an injection into the pericardium of Fiss. costaria, and that the coloured fluid had penetrated into the right kidney. This can be easily accounted for. The beginning of the right kidney lies immediately below the pericardium, and its cavity is only separated from that of the pericardium by the epithelium of the kidney, the exceedingly thin tunica propria of this gland, and the delicate wall of the pericardium. When an injection is forced into the pericardium under a high pressure—with a syringe, for instance— the liquid bursts through the wall of the pericardium and kidney at the point just mentioned. I have myself made the experiment. When using the method described in this paper such a thing never happened ; when, on the contrary, I used a syringe, I very often found the injection in one or the other kidney, sometimes in both, as they both come into the closest proximity with the wall of the pericardium. This place in both kidneys probably corresponds to the spot in which the nephridium was constricted off from the pericardium or coelom, and is very likely homologous to an abortive funnel in both cases.

I have been quite unable to find any trace of a reno-pericardiac canal like the one figured by Perrier (23) in pl. i, fig. 3, of his paper. The above-named gentleman, at my special request, has very courteously promised to look over his preparations, giving special attention to this point, but I have not yet received information as to the result.

I can also account for Bela Haller’s statements on the point at issue. The funnel he describes is nothing but the section of the aorta (compare his pl. i, fig. 1, with my own fig. 3, and Boutan’s [2] pl. xxiii, fig. 6). The renal end of his reno-pericardiac duct is nothing else than the genital duct (compare my fig. 18 with his fig. 2, pl. i). The same anatomist describes an entirely imaginary genital duct, which is only the inferior right mantle nook shown in my fig. 6. Had Haller carefully studied unbroken series of sections (he figures sections, but has probably not been able to cut complete series) he would certainly have avoided these mistakes.

Perrier certainly directed his attention almost entirely to the left kidney, rather neglecting the point whether a right reno-pericardiac duct really existed. The canal which he figures would be quite satisfactory were the opening into the kidney to be seen, which is not the case. He was evidently misled by Haller and by misunderstanding v. Jhering, who says that he could not satisfy himself as to the presence of a right reno-pericardiac duct. The latter information was obtained from Perrier’s answer to my letter.

Emarginula Houzardi.—The anatomy of this species, as seen after the removal of the shell through the very thin mouth, is illustrated in fig. 11. It closely resembles that of Fissurella. The right kidney, however, seems to be somewhat smaller than in Fissurella.

Fig. 27 is a perfectly transverse section through the pericardium and both kidneys of Emarginula. The external opening of the left kidney (XI) is very plainly seen in the section.

Puncturella spec.?—The same remarks I made about Emarginula can be applied to Puncturella.

Fig. 15 shows a transverse section through the pericardium and both kidneys of this species, which is certainly more primitive than Fissurella and Emarginula, as the visceral hump (fig. 22, H.) is much better developed here.

4. Patella cœrulea and Tectura spec.?

Special attention was given to Patella, as my results are absolutely contradictory to those of Ray Lankester (18, 19, 20) and Cunningham (6). Patella cœrulea is the only species of Patella found in the Gulf of Naples, and is the same which Cunningham has studied. I therefore do not doubt that the study of Patella vulgata would lead to the very same conclusions.

Perrier (23) has evidently neglected the right reno-pericardiac duct in Patella, as he neither describes nor figures it.

The shape and position of both renal organs are displayed in fig. 14, drawn from a hardened specimen after removal of the shell, hood, and dorsal pigment. The pericardium (Pe.) lies to the left and at the hinder end of the mantle cavity (Jf.). Its position and shape have been accurately described by Ray Lankester (loc. cit.) and Wegmann (28), who has written a short but valuable monograph of Patella vulgata, unfortunately paying but little attention to the relations of the kidneys and the pericardium.

The little or left kidney (Nl.) lies immediately to the left of the pericardium, between it and the right.kidney (Nr.), which covers very nearly the whole of the visceral mass. The papillæ of the kidneys lie on either side of the anus (A.) (Xr. and Xl.), and may be easily found when the hood or anterior mantle-flap has been removed.

Sections (transverse and horizontal) show that the kidneys are situated on either side of the rectum (R.) (fig. 25 a) (Nr. and Nl.). Their general histological appearance closely resembles that of Fissurella. It is a well-known fact that the rectum does not perforate the ventricle and pericardium in Patella, so that the rectum, the left kidney, and the anterior part of the right kidney are situated entirely to the left of the pericardium. The blood-sinuses of both kidneys are, as Perrier (23) has shown, in relation with the auricle of the heart, while in Fissurella, Haliotis, and Trochus this statement can only be applied to the left kidney.

As regards the presence or absence of reno-pericardiac ducts in Patella I have come to the same conclusions as for Fissurella, Emarginula, and Puncturella, and must also add Tectura to the list of Prosobrauchs having no communication between the kidneys and the pericardium.

Injections made according to my method, which I owe to Professor Mayer’s kindness, led me to the same conclusions. When a higher pressure is used the injection may penetrate into either kidney, but generally it is easier to drive it into the left. The places in which this happens are always the same, and can be readily found by dissections and sections without using injections.

Fig. 25a shows that towards the latter end of the mantle cavity (M.) the left kidney comes very near the wall of the pericardium. In this section there is still a thickish muscular partition between the left kidney (Nl.) and the cavity of the pericardium. This is the continuation of the partition between the mantle cavity and the pericardium. Still further back (fig. 255) the mantle cavity (M.) recedes more and more from the pericardium (Pc.), and the muscular partition entirely disappears in a spot (†) which very probably corresponds to an abortive funnel. In this place the cavity of the left kidney is only separated from that of the pericardium (Pc.) by the secreting epithelium of the kidney, the tunica propria of the same organ, and the flat epithelium of the pericardium. This accordingly is the likeliest spot for an injection to break through either from the pericardium into the left kidney or vice versâ. Even when using an immersion I was unable to find the smallest opening in this place when examining series of a specimen which had not been injected. I wish to remark here that Mr. Cunningham states that he has been able to trace the reno-pericardiac ducts in sections through an uninjected specimen.

I myself have already pointed out that to my mind the method of injection is of very small value in such cases, and very likely to mislead the investigator. I remind the reader that many Freuth anatomists, who seem to be particularly partial to injections, have, in molluscs, described a very complicated system of arteries, capillaries, and veins which were simply the artificial results of the injections.

A corresponding spot also exists in the right kidney, at the end of the so-called subanal tract of the right kidney (fig. 20). In this place, in which both Lankester and Cunningham have stated they found the reno-pericardiac duct, the right kidney also comes right up to the pericardium. It remains, however, separated from its cavity by a thin layer of muscular tissue. This circumstance explains why it is easier to get the injection from the pericardium into the left kidney than into the right renal pouch, and also accounts for the fact that Ray Lankester (18) first found the left kidney of Patella opening into the pericardium.

Tectura, as has already been mentioned, closely resembles Patella. There, nevertheless, are a few points on which I desire to direct the reader’s attention. As in Puncturella compared to Fissurella and Emarginula, the visceral hump is far better developed in Tectura (fig. 17, H.) than in Patella. Both in Tectura and Puncturella the difference in the size of both kidneys is smaller; both renal pouches are simple in their shape, that is to say, less ramified.

Fig. 24, a frontal section through the pericardium (Pe.) and both kidneys of Tectura, is given to show that the left kidney (A7.), which is still smaller than the right (Nr.), lies entirely to the front of the rectum (R.), and in the same longitudinal line as the right kidney. This fact will be made use of in the comparative part of this paper.

The results of this investigation may be summed up as follows :

Trochus, Turbo, and Haliotis possess a left reno-pericardiac duct only.

Fissurella, Emarginula, Puncturella, Patella, and Tectura possess no reno-pericardiac duct whatever, The genital products always pass through the right renal organ, either by bursting of the gonad through the walls of the right kidney, as in Patella and Trochus,1 or being admitted through a kind of valve (Haliotis), or transported to the right renal papilla by a special genital duct (Fissurella).

The inference to be drawn from these statements is that, according to the view first expressed by Ray Lankester (19), the only remaining nephridium of most Prosobranchs corresponds to the actual left kidney of forms possessing two renal organs. In my paper on the development of Paludina (8) I have stated that this view was supported by embryological evidence, the actual nephridium of Paludina being situated before the torsion to the right of the anus, while the rudiment of the actual right kidney lies to the left of the rectum before the torsion takes place. I have further shown that, as Sarasin2 had already stated, the actual nephridium in Bythinia tentaculata was, before the torsion, situated to the right of the anus, as must be the case in all leiotropic forms. In Pl an or bis, on the contrary, which is a dexiotropic species of fresh-water Pulmonates, the actual right nephridium is, before the torsion, situated to the left of the rectum (10).

‘These facts, compared with the fact that the genital gland in the above-mentioned species of Zygobranchs and Cyclobranchs, or, according to the new French terminology (3), Diotocards and Heterocards, opens into the right kidney, and that in Paludina the duct of the rudimentary right kidney becomes the genital duct, show clearly—

  1. That the only remaining kidney in most Prosobranchs is the actual left one.

  2. That the actual right kidney has disappeared or become transformed, and that a part of it corresponding to the duct forms a part of the genital apparatus.

The next question is, what has become of the glandular part of the actual right kidney ? R. Perrier (23), in his extensive memoir on the anatomy of the kidneys of Prosobranchs, came to the conclusion that the only remaining kidney of most Prosobranchs is homologous with the actual right kidney of those forms which are provided with two renal organs. He inferred this from the fact that the actual right kidney of birenal forms is always the larger one, and always shows the characteristic brown renal secretory epithelium. I have already given my reasons against this inference, and will add that it seems more rational to admit that all the organs of the actual right side (left before the torsion) have disappeared in higher Prosobranchs. This opinion is supported by the facts that in Haliotis the right ctenidium is smaller than the left, and that in Turbo and Trochus the only remaining ctenidium and auricle are the actual left. R. Perrier says that the actual left kidney, which is fast disappearing in Fissurella, much reduced in Patella, and highly modified in Haliotis, Trochid æ, and Turbo, where it is called papillary sac, has transformed itself into the so-called nephridial gland, a distinct part of the only remaining kidney of most Monotocards.

According to Perrier the transition between Diotocards and Monotocards is formed by the Patellidæ or Heterocards. The left kidney has become located between the pericardium and the right kidney. The sinuses of both kidneys are in communication with those of the auricle. Supposing, says Perrier, that the thin wall between the left and the right kidney in Patella disappeared, the left kidney would become part of the right kidney ; thus apparently there would be only one kidney remaining, and the left one would exactly correspond to the nephridial gland. This hypothesis is realised by Ampullaria,1 which, according to Bouvier (4), shows two kidneys, of which the actual right one (according to Bouvier) has the same shape and position as (ex. gr.) the only remaining kidney of Paladina, and opens into the mantle cavity; the other one (left according to Bouvier) has no external opening, but communicates with the other renal organ. Whilst the first renal organ is formed of lamellae, the roof of the second one is coated with a vascular web, which constitutes the renal tissue.

The vascular irrigation of the first kidney is the same as in the renal organ of Lamellibranchs, as the venous blood which has passed through it goes to the gills before reaching the heart, whilst the venous blood of the second flows directly into the auricle.

“The two renal organs of Ampullaria are, therefore (says Bouvier), placed exactly in the same conditions as those of Haliotis, according to Wegmann’s description, the second kidney performing the same part in the circulation as the only kidney of Monotocard Prosobranchs.”

Bouvier, therefore, argues that the first kidney is homologous with the right kidney, the second with the left kidney of Diotocards.

I myself hold the opposite view on the same subject. Bouvier’s most valuable argument is derived from the circulation in the renal organs. Perrier (23), however, has shown that, as we proceed higher in the series of Prosobranchs, the circulation in the kidney undergoes very considerable changes. The quantity of blood passing through the right kidney before going to the gills decreases more and more as we proceed from Haliotis to Trochus and Turbo. In Monotocards the only remaining kidney has developed an entirely new and different system of blood-irrigation, and its circulation has grown quite independent of the general one. His argument, therefore, turns out to be much less important than it seemed at first.

The position of the kidneys, as far as I can make out by examining the figure given by Bouvier of a dissected Ampullaria, would rather tend to prove that the large vascular sac lies more to the right, the smaller lamellar organ to the left of the rectum and the body axis. The size and shape of both kidneys further supports my own view. The lamellar organ closely resembles the kidney in the embryo of Bythinia, as described by myself (9), while the size of the left kidney and the simplicity of its structure strongly remind one of the right renal organ in Diotocards and Heterocards.

I must now beg the reader to refer to my fig. 24 of Tectura species which shows that the left kidney (the small one) lies quite anteriorly to the large right one, a fact which might explain the position and homologies of the renal organs of Ampullaria, further supporting my own view on the subject.

Bouvier, whose abilities as an anatomist I value most highly, has only examined specimens of Ampullaria preserved in spirit, and exclusively made use of the method of dissection. I must venture, therefore, on technical grounds, to question some of his statements. It seems highly improbable to me that the lamellar renal organ should have no communication with the pericardium, whilst the kidney of Bythinia, which is closely similar to it in shape and texture, clearly shows a well-defined reno-pericardiac duct. This point, and the communication of the two renal organs, ought certainly to be reinvestigated in well-preserved specimens by the method of sections. Bouvier has shown and stated that the organisation of Ampullaria closely resembles that of Paludina. Ampullaria (says Bouvier) is a large Paludina, which by adaptation to a new mode of life has acquired a lung. The results obtained by the study of the development of Paludina may therefore safely be applied to Ampullaria, all the more as the species described by Bouvier is leiotropic like Paludina. I consequently am quite convinced that the lamellar kidney of Ampullaria is homologous with the actual left kidney of Paludina, the vascular sac in Ampullaria to the rudimentary right kidney in Paludina.

Before taking leave of the kidneys of Prosobranchs, I must yet mention the curious organ in Dolium described by P. Schiemenz (26) under the name of anal kidney (Afterniere). This organ consists of two brown glandular lobules situated on either side of the anus : they have been described by Haller (13). On their surface can be descried numerous canals, having the appearance of blood-vessels. These canals, however, are by no means blood-vessels. They unite from both sides and run into a large sinus which envelops the rectum. The sinus opens to the right of the anus by a large lip-like orifice. This opening must not be mistaken for the female genital opening, which lies to the left of it. The anal kidney does not communicate with the pericardium, while the actual left kidney is plainly seen to possess a reno-pericardiac duct.1

In this instance also it would be highly desirable to study the development of the left kidney, and of the anal kidney of Dolium, as under the present state of our knowledge it is doubtful, although probable, that the so-called anal kidney really represents the modified right kidney of Dolium.

To return to R. Perrier’s hypothesis, this author is ready to admit that his ideas on the homology of the only remaining kidney of Monotocards can easily be reconciled with my own. He was led to believe that one kidney had disappeared in these forms. The only circumstance which induced him to suppose that the remaining kidney was the actual right nephridium was the predominance assumed by the right kidney in Diotocards, an argument derived from analogy, and “peu probant,” as Perrier himself wrote to me. It would be necessary to ascertain whether the nephridial gland really represents one or the other kidney. I hope to be able to solve this problem in the course of time, having already collected materials for the study of the development of Cass id aria, which Perrier chose as a type for his description of the nephridial gland. If according to Perrier the nephridial gland represents the actual left nephridium, we should be led to conclude that in Paludina and Bythinia, where no such gland exists, the actual right kidney has disappeared, and the remaining left is homologous with the nephridial gland of other Monotocards.

To the best of my knowledge, it is more probable that in most Monotocards the actual right kidney has disappeared, and that possibly it has been transformed into Perrier’s nephridial gland.

A. Lang, in a short pamphlet purposing to explain the asymmetry of Gastropods by mechanical processes, has also arrived at the conclusion that in Monotocards the whole actual right complex of originally paired organs has disappeared. This pamphlet is evidently the result of Lang’s study of literature previous to the publication of the part of his textbook of comparative anatomy dealing with molluscs. Whilst most of the ideas expressed in Lang’s paper are certainly not new, his mechanical explanation of the asymmetry is certainly very ingenious. Biitschli, the last zoologist who dealt fully with the same question, had not attempted a mechanical explanation of this difficult problem. Unfortunately several facts are a serious impediment to Lang’s theory. For instance, it is difficult to understand why Trochus and Turbo, the shells of which are just as highly coiled as that of the common snail, should have retained two auricles and two kidneys if the pressure brought to bear by the shell on the actual right side of the body is held to have caused the disappearance of the corresponding set of organs. Our present knowledge of the development of Fissurella and Patella, which we owe to Boutan (2) and Patten,1 is another serious objection, as it is well known that the shell of both these species is originally nautiloid.

Another point which seems not to have met with any attention from Professor Lang is that up to the present it must have seemed highly probable that Perrier’s view on the homologies of the only remaining kidney in Monotocards, viz. that it represented the actual right one of Diotocards, must be correct. Lang neither mentions Perrier’s exhaustive treatise nor my own paper on the development of Paludina, in which I was the first to maintain the opposite view.

Of course, I am quite prepared to admit that many facts and statements must needs escape the attention of the author of a text-book comprising the whole of the animal kingdom, especially when the writer had not previously himself worked for some time upon the group he describes.

I now propose to compare the results afforded by the study of Prosobranchs with those obtained by other workers from the remaining groups of Gasteropods and molluscs in general.

The Heteropods are now almost generally considered as modified Prosobranchs. As was to be expected accordingly, the nephridium is situated to the left of the anus and rectum.

We now come to the so-called Euthyneura. I have already stated that the development of Planorbis (10) confirmed my view of the homologies of the only remaining nephridium, which is also supported by the evidence collected from several other papers by different investigators dealing with the same question1 with regard to Pulmonat es. Of all Opisthobranchs, the Tectibranchiata are certainly the least modified forms and the most nearly related to Prosobranchs. The anatomy and a part of the embryology of Aplysia has been recently studied by my friend Signor Mazzarelli. According to him the external opening of the renal organ in the adult lies ventrally and to the left of the anus and rectum. The kidney in the larva or veliger stage most probably corresponds to an organ which has been described as an eye by Lacaze-Duthiers. The position of the organ, which in the larva lies to the left of the rectum and anus (after the torsion has taken place in a leiotropic direction), shows that it must be the actual left kidney. The development shows that the mode of formation of this organ closely agrees with that of the kidney of Paludina, Bythinia, and Planorbis. Before the torsion it lies to the right of the rectum. Its glandular part has a mesodermic origin; the duct is formed by a short invagination of the ectoderm. The external opening is clearly seen in the veliger stage to the left and a little below the anus. According to Signor Mazzarelli there is even evidence to prove that a similar but rudimentary renal organ was, before the torsion, situated to the left of the rectum.

In Pulmonata and Tectibranchiata the torsion (leaving out of account the torsion of the visceral hump, which is an independent process [Biitschli] from that of the general torsion) is already less marked than in Prosobranchia. The original twisted condition is still more reduced in Pteropoda and Nudibranchiata, where a kind of untwisting has very probably taken place. This explains why the actual left kidney (the right one before the torsion) apparently does not occupy the same position as in Gasteropods, though in reality its position is homologous, provided we suppose that a secondary untwisting has taken place to a greater or lesser degree.

In all other groups of Mollusca, that is to say, in Placophora, in Scaphopoda, in Lamellibranchiata, and Cephalopoda, the renal organ is paired.

I have not yet mentioned the Aplacophora or Neomenia, as Pruvot (25) has recently thrown considerable doubt on Hubrecht’s (15) views on the morphology of the uro-poetic apparatus in this interesting group. Pruvot considers the ducts leading from the pericardium (Hubrecht) as nothing but oviducts, the pericardium itself as a mere egg-pouch. The unpaired glandular part, considered by Hubrecht as the secreting part of the nephridia, is called a shell-gland by the French anatomist. Pruvot describes as an excretory gland a new organ which he calls the cloacal ridge (bourrelet cloacal).

I cannot attempt to explain away Pruvot’s statements concerning the secreting part of the kidney, not having studied myself the anatomy of Neomenia. However, I think that this can be easily done for the pericardium and ducts of the nephridia.

Pruvot, after having in a preliminary account of his investigations denied that the organ hitherto described as heart really represented the blood-propelling organ, has in the full account of his researches admitted that the heart really exists, but in a very rudimentary form. Nevertheless he refuses to admit that the pouch, in the roof of which the heart forms a gutterlike invagination, really represents the pericardium. His chief objection is that the epithelial lining of this pouch produces the ova and the spermatozoa. The conception that the cavity of the pericardium in molluscs represents the reduced cœlom, and that the cavity of the gonad originally formed a part of this cœlom, is evidently unknown to Mr. Pruvot. The fact that the epithelial lining of the pericardial cavity represents the gonad or genital epithelium is the best proof that the Neomenia show a very primitive condition in this point, reminding one strongly of the condition to be met with in a great number of Annelids. I therefore further conclude that Pruvot’s oviducts are really the nephridial ducts which possibly have lost their connection with the glandular part of the renal organ.

Having discussed Pruvot’s rather isolated conception of the uro-poetic organs of Neomenia, I think it advisable to compare the results which I have obtained by the study of Prosobranchs with those of other anatomists on the corresponding organs of the remaining molluscs.

In an account of the development of Paludina I have shown that the gonad arises as an évagination of the pericardium or coelom, which gradually becomes constricted off and acquires a special duct leading into the mantle cavity. The glandular portion of both renal organs has a similar mode of formation, and the original lumen of the évagination leading into the pericardium becomes the reno-pericardiac funnel. The cavity of the gonad and those of both nephridia are, therefore, parts of the cœlom.

In Paludina the actual right kidney has disappeared, and its duct, formed by an introflection of the ectoderm, becomes the efferent duct of the gonad. The actual left kidney persists, and remains in communication with the pericardium.

The history of the development will explain the facts wt have met with in the anatomy of the forms dealt with in thii paper. In Fissurella and allied forms, as well as in Patelle and Tectura, both renal organs have lost their communication with the part of the cœlom represented by the pericar dium. The shape and size of the right kidney, and the way il extends between all viscera, pervading the whole body oi Fissurella and Patella, are explained when we consider ii as a part of the cœlom. The fact that the nephridia in Fissurellidæ and Patellidæ have lost their communication with the pericardium is certainly surprising, especially as no other such cases are known in molluscs. In other groups, however, we meet with parallel cases—so, for instance, in Hirudinea, in which most species have lost the opening of the nephridia into the cœlom. Besides, it must be remembered that both Fissurella and Patella, which by reversion to the primitive external symmetry have regained or preserved to a great extent the original internal symmetry, are in reality highly modified forms. This is abundantly shown by the story of the development of the shell (loc. cit.).

I will now attempt to give an idea of the condition of the uro-poetic apparatus in the hypothetical ancestral form of molluscs, and to show how the present condition in actual living groups can be easily deduced therefrom (see diagram). It is now a view accepted nearly by all morphologists, that the ancestral form of molluscs was of bilaterally symmetrical build, and that the anus (A.) and mantle (M.) cavity were situated at the aboral end of the animal. Spengel,1 Bütschli (5), Ray Lankester (21), Lang (17), and others have built up their theories on the asymmetry and torsion on this hypothesis. The existence of the bilateral symmetry further implies that the ancestral form possessed paired ctenidia (Br.), osphradia, and nephridia (N.). The nephridia were tubes with a medium glandular portion having a communication (Y.) with the pericardium (Pc.), and opening at the basis of either ctenidium at the end of a papilla (P.). The rectum (R.) passed through the pericardium (Pc.), but ventrally from the heart, without perforating the ventricle (V.), opening by the

Diagram of the reno-pericardial system of the ancestral form of molluscs. ao. Aorta. au. Auricles. Ma. Mantle. The other letters are explained in the text.

Diagram of the reno-pericardial system of the ancestral form of molluscs. ao. Aorta. au. Auricles. Ma. Mantle. The other letters are explained in the text.

anus (A.) in the middle line, at the bottom of the mantle cavity (M). Most probably the entire anterior half of the epithelial lining of the pericardium, that is to say, the portion anterior to the region occupied by the heart, represented the gonad (G.). The sexual products dropped into the cavity of the pericardium passed through the funnel into the nephridium, and passed out of the nephridial duct into the mantle cavity. This condition would be nearly realised by the actual Neomeniæ.

Very soon the portion of the pericardium, the lining of which represented the epithelium of the gonad, became constricted off the pericardium (compare the development of Paludina). This is the case in all other groups of Mollusca except Neomeniæ.

According to Pruvot, the gonad in Aplacophora is formed by two symmetrical portions only separated by a ridge. The gonad is unpaired in Placophora, Cephalopods, and Gasteropoda. These certainly being less modified forms than Lamellibranchiata and Scaphopoda, where the gonad is paired, it is reasonable to infer that the original condition was an unpaired gonad. This having become separated off from the pericardium was accordingly obliged to form a new communication with the outer world. In Zygo-branchs, Tectibranchs, and in Scaphopods the gonad enters into communication with the actual right nephridium by bursting open its”wall, or by opening into it by a special duct, probably evolved from a part of the gonad itself. In higher Prosobranchs the genital duct is probably the duct of the actual right aborted kidney (Paludina). In the archaic forms of Lamellibranchiata, which according to Pelsener (22) are modified Prosobranchs, such as Nucula, the genital products are expelled into the initial part of the nephridia, that is to say, alongside of the reno-pericardiac funnel, while as we proceed higher, independent genital ducts are formed. In Chitons we find an independent pair of genital ducts, as in Cephalopods. It is as yet not known whether these ducts are in any way related to those of the nephridia.

According to Grobben (12), Sepia, probably the most archaic form, shows a large cœlom, communicating with the nephridia by two openings or funnels. The cavity of the cœlom is coated with an epithelium, and encloses in its anterior portion the heart with its vessels, the branchial hearts and the pericardial gland, formed by differentiated peritoneal epithelium. The hinder portion of the cœlom, divided off incompletely from the anterior one by a septum, encloses the gonad, which probably belonged originally to the epithelium of the peritoneum, and the stomach.

All the evidence which I have collected in the comparative part of this paper tends to show that the molluscs are true cœlomate animals, and that the condition of the genital and renal organs is closely similar to that of primitive Annelids.

Before concluding this paper I wish to remark that I am fully prepared to have the truth of my statements on Fissurella and. Patella questioned. I have given myself the greatest trouble to find both reno-pericardiac ducts. Being unable to see the left one, the existence of which I was most anxious to prove for reasons which the reader of this paper will easily understand, I began to look for the right one. I thought that, having once found the right one, its shape and position would enable me to see the left one. Meeting with the same negative results, I then examined Haliotis and Trochus, when I immediately found the left reno-pericardial duct only, but this with the greatest ease. I then carefully re-examined my preparations of Fissurella and Patella, and came to the results which I have fully described in this paper. I next considered it my duty to explain the contradictory statements of my predecessors, and hope to have done this successfully. Nevertheless I will be most happy to confess that I have been wrong in this matter, provided I am shown an uninterrupted series of sections through an uninjected specimen displaying one or both reno-pericardiac ducts in Fissurella or Patella. A valid proof of the existence of both reno-pericardiac ducts in both these species would exactly suit my theory on the homologies of the kidney in Monotocards.

In my paper on Bythinia I have fully expressed the opinion I hold on the value of the method of sections. I have stated that in my humble opinion a thorough study of the entire animal or embryo by other methods must always precede that of sections. However, I maintain that sections alone can, under the present state of anatomical technique, give us an exhaustive knowledge of complicated topographical questions and of delicate anatomical points. The method of sections is most valuable when the existence of a communication between an organ and another organ or the outer world is to be proved. In this case sections are the only true test. My figures show that when a reno-pericardiac opening really exists it has the shape of a well-defined canal, generally of no inconsiderable length, as in Haliotis and Trochus. I have seen the same structure in Paludina, Bythinia and Aplysia, in Signor Mazzarelli’s series of sections. For these reasons I think it is fair that I should require to be shown similar ducts in Fissurella and Patella beforel give up my own view on the points I have discussed in this paper.

It is my pleasant duty to thank the Office of Public Instruction of Baden for the table which it generously placed at my disposal, hereby enabling me to make further researches on the comparative anatomy and embryology of molluscs. The excellent organisation which the Zoological Station of Naples owes to its director, Professor A. Dohrn, always kept me supplied with an abundance of material. I must specially thank Sr. Lo Bianco for the trouble he took in procuring for me the numerous specimens which I required for my researches. I am further indebted to Professors Eisig and P. Mayer for valuable technical hints, and to my friend Mr. MacBride, who kindly undertook to read the manuscript of the first paper which I have published in the English language.

Naples Zoological Station ;

April 9th.

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I have lately examined Trochus and Turbo, in order to test v. Jhering’s and B. Haller’s statements about the existence of a proper genital duct (loc. cit.).

V. Jhering’s figure is absolutely schematic, and is not accompanied by a detailed description. As he failed to recognise the existence of the left kidney, it is highly probable that he mistook one or the other renal duct for the genital duct.

Haller simply mistook the right renal duct for a proper genital duct, having stated that the right kidney opened into the left one.

I was unable to find any proper genital duct in Trochus turbinatus and Turbo rugosus, although I used both the method of dissection and that of unbroken series of sections.

On the other hand, the appearance, position, and the vicinity of the genital gland to the glandular portion of the right kidney and the beginning of the right renal duct are the same as in Haliotis. I am therefore led to the conclusion that the sexual products are expelled by the right kidney.

Should this conclusion be correct (an absolute proof can only be given by finding ova or sperma in the right renal duct), all primitive Prosobranchs would be devoid of a proper genital duct, the right renal duct serving also as a genital duct. In higher developed forms the glandular portion of the right kidney has disappeared, whilst its duct forms a part of the proper genital duct.

For the present I can only say that, contrary to v. Jhering’s and B. Haller’s assertions, there is no proper genital duct in Turbo and Trochus.

Naples ; June 1,1892.

Ilustrating Dr. R. v. Erlanger’s paper “On the Paired Nephridia of Prosobranchs.”

List of Reference Letters

A. Anus. Ap. Anal papilla. Au. Auricles of the heart, aur. Right ; aul. Left auricle, ao. Aorta. B. Gill (ctenidium). Br. Right ; Bl. Left ctenidium, bas. Basibranchial sinus. bs. Branchial rod or support. C. Reno-pericardiac canal. E. Eye. F. Foot. Fi. Mantle-fissure. G. Gonad genital gland. Gd. Genital duct. H. Visceral hump. Ha. Heart. I. Intestine-gut. L. Liver. M. Mantle cavity. Ma. Mantle. Mb. Bottom of the mantle cavity. Msr. Right superior portion ; Msl. Left superior portion ; Mir. Right inferior portion ; Mil. Left inferior portion of the mantle cavity. muc. Mucous gland, mu. Muscle. N. Nephridium. Nr. Right; Nl. Left nephridium-papillary sac. P. Papilla of the nephridium. Pr. Right ; Pl. Left papilla. Pc. Pericardium. R. Rectum. S. Stomach, si. Sinus. V. Ventricle of the heart, ve. Vein. vt. vena transversa, vbe. Branchial efferent vein. X. External opening of the nephridium. Xr. External opening of the right ; Xl. External opening of the left nephridium. Y. Opening of the nephridium into the pericardium, y. Opening of the reno-pericardiac canal into the pericardium.

FIG. 1.—Dorsal view of Haliotis tub. after removal of the shell, .

FIG. 2.—Dorsal view of Haliotis tub. The mantle cavity has been opened, the rectum and the mucous gland thrown back, so as to display the external openings of the kidneys, .

FIG. 3.—Pericardium of Haliotis tub. opened; heart removed. The front wall of the pericardium is seen from behind, and shows the left kidney by transparency, and the inner opening of the reno-pericardiac duct.

FIG. 4.—Mantle cavity of Trochus turb., opened and extended. Ventral view of thq gill, pericardium, nephridial ducts, and rectum.

FIG. 5.—Pericardium of Fissurella cost., opened dorsally ; heart cut out. Both kidneys seen in situ by transparency, .

FIG. 6.—Mantle cavity of Fissurella cost., in transverse section, displaying the shape of the mantle cavity, the position of the gills, anus, nephridial papillæ, and basibranchial sinus.

FIG. 7.—Transverse section through the pericardium and both kidneys of Trochus turb., showing the reno-pericardiac canal.

FIG. 8.—Transverse section through the basibranchial sinus and both kidneys of Trochus turb., showing the reno-pericardiac canal.

FIG. 9.—Horizontal section through the pericardium and both kidneys of Halietis tub.

FIG. 10.—Ventral view of the mantle cavity and pericardium of Fissurella max. The pericardium is opened ventrally; the heart is displayed, .

FIG. 11. Dorsal view of Emarginula Huzardi, after removal of the shell. Anatomy seen by transparency through the mantle, .

FIG. 12.—Transverse section through the basibranchial sinus of Trochus turb.,showing the reno-pericardiac canal opening into the pericardium.

FIG. 13.—Transverse section through the basibranchial sinus of Trochus turb., showing the reno-pericardiac canal opening into the left kidney.

FIG. 14.—Dorsal view of Patella coer, after removal of the shell, pigment, and hood ; displaying the relations of the pericardium and both kidneys, the papillæ of the anus and both kidneys, .

FIG. 15.—Transverse section through the pericardium and both kidneys of Puncturella spec.

FIG. 16.—Transverse section through the pericardium of Fissurella gibb., showing the right kidney opening into its papilla.

FIG. 17.—Tectura spec.? viewed from the left side after removal of the shell, showing the position of the pericardium. .

FIG. 18.—Papilla and genital duct of Fissurella cost., cut transversely and viewed from behind ; a bristle has been introduced into the genital duct, and comes out through the duct of the right kidney. .

FIG. 19.—Left kidney of Fissurella cost., dissected out. .

FIG. 20.—Transverse section through the pericardium and subanal tract of the right kidney in Patella coer.

FIG. 21.—Transverse section through the right renal papilla and genital duct of Fissurella gibb.

FIG. 22.—Puncturella spec.? viewed from the left side after removal of the shell.

FIG. 23.—Transverse section through the pericardium and both kidneys of Pissurella græca. .

FIG. 24.—Horizontal section through the pericardium and both kidneys of Tectura spec.

FIG. 25 a.—Transverse section through the pericardium and both kidneys of Patella coer.

FIG. 25 b.—Transverse section through the pericardium and the left kidney of Patella coer. .

FIG. 26.—Transverse section through the right kidney of Fissurella nubecula, showing the genital duct opening into the right kidney, which also contains eggs.

FIG. 27.—Transverse section through the pericardium and both kidneys of Emarginula Huzardi. .

Lenses and eye-pieces used with Abbé’s camera lucida.—Zeiss, oc. 1 (achr.), obj. a3 (achr.) = . Zeiss, oc. 1 (achr.), obj. 16 mm. focal distance (apochrom.) = . Zeiss, 2 (apochrom.), obj. 16 mm, focal distance (apochrom.) = .

The above-mentioned eye-pieces and lenses were used for the drawing of the figures of microscopic sections ; the whole series of the apochromatic objectives, 8 mm., 4 mm., and 2 mm. immersion, were used during the course of this investigation, with apochr. eye-pieces 6 and 8. The drawings of dissected specimens were done with Nachet’s dissecting stand and a camera lucida.

1

Leiotropic would correspond to the German term “rechtsgewunden,”as used by conchologists ; dexiotropic to “linksgewuuden.”

1

Sublimate 5 per cent, in sea-water 3 parts, and 1 part of glacial acetic acid,

1

Pelsener (22) has found the left kidney in Scutum (Parmophorus).

1

In Turbo and probably also in Trochus, the genital gland has a separate opening into the mantle cavity (v. Jhering (16), and “Sur les relations naturelles des Cochlides et des Ichnopodes,” in ‘Bulletin scientifique de la France et de la Belgique,’ xxiii, J. Partie, 1891, pp. 148—257, pl. iv—vi).

2

Sarasin, P., “Entwickelungsgeschichte derBythinia tentaculata,” in ‘Arb. z. Inst. Wurzburg,’ Bd. vi, 1882, pp. 1—68, Taf. i—vii.

1

The species examined was leio tropic.

1

Dr. Schiemenz had the kindness to show me the organ just described in several specimens of Dolium preserved in spirits.

1

Patten, “The Embryology of Patella,” in ‘Arb.Zool. Inst. Wien,’ Bd.vi, 1885, pp. 149—174, Taf. xiv—xviii.

1

I must refer the reader to the list of embryologieal papers given in my memoir on ‘Paludina’ (8).

1

Spengel, J. W., “Die Geruchsorgane und das Nervensystem der Mollusken,” ‘Zeitschr. f. wiss. Zool.,’ 1881, xxxv, pp. 333—384, Taf. xvii—xix.