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On the Paired Nephridia of Prosobranchs, the Homologies of the Only Remaining Nephri- Dium of Most Prosobranchs, and the Re ON THE PAIRED JSTEPHRIDIA OF PEOSOJ3RANCHB. 587 On the Paired Nephridia of Prosobranchs, the Homologies of the only remaining Nephri- dium of most Prosobranchs, and the Re- lations of the Nephridia to the Gonad and Genital Duct. By Dr. R. v. Erlanger. With Plates XXXVI and XXXVII. INTRODUCTORY AND HISTORICAL PART. BY the study of the development of Prosobranchs and fresh-water Pulmonates, especially of Paludina vivipara (8), Bythinia tentaculata (9), and Planorbis corneus (10), I was led to adopt Professor Eay 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 Fissnrella, 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 1 Leiotropic would correspond to the German term "rechtsge- wunden,"as used by ooncliologists ; dexiotropic to " linksgewunden." 588 DR. E. V. EB.LANGER. this fact with the statement that the right kidney of Zygo- branchs 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 Gastro- pods, I was struck by the contradictory statements about the reno-pericardiac duct in Zygobranchs, Cyclobranchs, and Prosobranchs. Ray Lankester, in his first paperonPatella (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 communi- cation between either kidney and the pericardium in Fissurella 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 Pissurella, and could not find a reuo-peri- cardiac canal in the right kidney. B. Haller (13) describes a right reno-pericardiac duct in Pissurella. Wegmann does not mention any communication for either kidney and the pericardium in Patella (28), although he found a left reno- pericardiac duct in Haliotis (27), where the right kidney has no opening into the pericardium. Cunningham (7), at Ray Laukester'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. Ou the other hand, he found only a left pericardiac duct in Haliotis, Trochus, and Turbo. The conclusion to be drawn from this historical resume 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, aTectura, one species of Haliotis, one of Trochus, and a Turbo. My results, as the sequel will show, are somewhat surprising as regards Fissurella and ON THE PAIRED NEPHRIDIA OF PROSOBRANOHS. 589 Patella, whilst they only confirm prior investigations as regards Haliotis, Trochus, and Turbo. I further hope to offer a plausible explanation for the con- tradictions 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 I 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 Fleraming'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 Bianco3 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 puU 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 1 Sublimate 5 per cent, in sea-water 3 parts, and 1 part of glacial acetic acid, 590 DB. E. V. ERLANOER. 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 hsematoxylin 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 speci- men 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 embed- ding was done in chloroform and paraffin. Besides dissec- tions 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 solu- tion 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 con- trary, 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 resis- tentiae, and which shall be described in the sequel. Before beginning my correspondence with Professor Bay 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, ON THE PAIEED NEPHRIDTA OF PROSOBEANOHS. 591 and consequently in a centrifugal direction. By request of Professor Ray Lankester, 1 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. TCobelt, in Schwanheim, near Frankfort-on-the-Main. I beg both these gentlemen to accept my thanks for having so readily fulfilled my request. DESCBIFTIVE PART. 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), Weg- mann (37), Haller (13), and Perrier (23). I am happy to be able to confirm Jhering's, "Wegmann's, and Perrier's state- ments.
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