Cat Kidney Glomeruli and Tubules Evaluated by Design-Based Stereology

Renal function is related to its structure and three-dimensional structural parameters correlate better with the kidney function than two-dimensional structural parameters. Stereology is the current gold-standard technique for the morphometrical evaluation of kidney structures. This study describes morphometric features of the kidney of the cat using design-based stereological techniques aimed to introduce the cat as a translational model in nephrology and provide basic findings for diagnosis and treatment of kidney diseases in this species. Left kidneys of four cats were included in the present study. The kidney volume, volume fraction of cortex and medulla, glomerular volume, glomerular mean volume, glomerular number, and proximal convoluted tubule (PCT) and distal convoluted tubule (DCT) length were estimated. The kidney volume was estimated to 11.4 ± 1.3 cm³. The volume fraction of cortex and medulla was 65.6 ± 2% and 34.2 ± 2%, respectively. The total number of glomeruli was estimated to be 186 ± 11 × 10³ using the physical disector/fractionator method. The mean glomerular volume was estimated to be 1.54 ± 0.06 × 10⁶ μm³ and the glomerular volume was covering 2.13 ± 0.34% of the whole kidney. The total length of PCT and DCT was estimated to be 2.26 ± 0.48 km and 505 ± 43 m, respectively. Our data might contribute to the knowledge of kidneys in mammals and provide a comparison with available data on human and other mammals. Anat Rec, 302:1846–1854, 2019. © 2019 American Association for Anatomy     

Structure of the avian kidney

The kidneys from 6 domestic fowl were fixed in situ by perfusion from the left ventricle. In the bird there are two types of nephrons. One reptiliantype without Henle's loop and medullary tissue, and one mammalian-type with Henle's loop lying in medullary tissue. Serial sections from kidney tissue embedded in plexiglass or in paraffin were used to study the architecture of eight reconstructed reptilian-type nephrons from different cortical levels. All reconstructed nephrons had four major bends, but particularly in the subcapsular nephrons additional bends parallel to the kidney surface were found. There was no loop of Henle, but before entering the collecting duct the distal tubule usually had a very thin-walled segment. No proximal convoluted part was found in the reptilian-type nephrons. The length of the tubules varied between 3,000 μm and 6,000 μm. In the distal tubule a macula densa segment was found in all nephrons of the reptilian and mammalian type. The capillary network between the inter- and intralobular veins was composed of increasingly larger capillaries towards the intralobular vein. Segments of the distal tubule were indented into these capillaries and completely surrounded by them. In the nephrons of the mammalian type the proximal tubule was found to be convoluted as is usual for mammalian species.     

锌转运体-1在小鼠肾脏的表达

目的研究锌转运体-1(zinc transporter1,ZnT-1)在小鼠肾脏的定位分布。方法应用免疫组织化学技术和免疫印迹技术检测小鼠肾脏中ZnT-1的分布。结果 ZnT-1在肾脏内有丰富表达,其主要分布于远曲小管上皮细胞的近腔侧和基底侧的细胞膜上,而在肾小体、肾小管的其它部分以及髓质中的分布较少。结论小鼠肾脏内含有丰富的ZnT-1,ZnT-1可能参与了锌离子在肾脏的排泄和重吸收过程。     

硒酸锌金属自显影技术检测游离锌离子在小鼠肾脏的分布

目的研究游离锌离子在小鼠肾脏的定位分布。方法应用硒酸锌金属自显影技术(ZnSeAMG)检测小鼠肾脏内的游离锌离子分布。结果游离锌离子在肾脏内分布广泛,皮质中有大量AMG反应阳性颗粒,髓质中的AMG阳性颗粒较少。其中,近曲小管、远曲小管、近直小管和远直小管上皮细胞近腔侧均分布有大量的棕黑色AMG阳性颗粒,肾小体、细段和集合管上皮细胞中AMG阳性颗粒较少。结论小鼠肾脏内含有丰富的游离锌离子,锌离子可能参与肾脏的功能。     

Survey of the morphology of the dog kidney

Dogs are frequent subjects in experimental studies of renal physiology and pathology in spite of the paucity of information on their normal renal morphology. In this study, gross morphology, light microscopy, and scanning and transmission electron microscopy were used to describe dog renal anatomy. The dog has a multilobed kidney with the medulla fused into an elongate crest and a renal pelvis of elaborate shape. The outer zone of the medulla lacks a definitive outer stripe. The proximal tubule consists of four distinct anatomical segments. Dark cells are abundant in the collecting duct of the inner medulla. The majority of the nephron segments demonstrate remarkable similarities to those of the human kidney and less to those of the kidney of the laboratory rat.     

Survey of the morphology of the dog kidney.

Dogs are frequent subjects in experimental studies of renal physiology and pathology in spite of the paucity of information on their normal renal morphology. In this study, gross morphology, light microscopy, and scanning and transmission electron microscopy were used to describe dog renal anatomy. The dog has a multilobed kidney with the medulla fused into an elongate crest and a renal pelvis of elaborate shape. The outer zone of the medulla lacks a definitive outer stripe. The proximal tubule consists of four distinct anatomical segments. Dark cells are abundant in the collecting duct of the inner medulla. The majority of the nephron segments demonstrate remarkable similarities to those of the human kidney and less to those of the kidney of the laboratory rat.     

Histogenesis of the loop of Henle in the rat kidney

Summary The epithelial differentiation of the loop of Henle was investigated in the kidneys of Wistar rats between embryonic day 15 and postnatal day 30. Three stages can be distinguished in the development of the loop of Henle: (1) the primitive loop, (2) the immature loop and (3) the mature loop. The primitive loop of Henle is composed of thick undifferentiated tubule epithelium and is divided into a strongly basophilic proximal tubule anlage that stains dark in the semithin section, and a weakly basophilic, light-staining distal tubule anlage. The two anlages are separated by a cytologically sharp boundary located in the descending limb just before the bend of the loop. The immature loop of Henle is present when differentiation of the tubule epithelium begins. The shorter initial portion of the proximal tubule anlage develops into proximal straight tubule epithelium with brush border, brush border enzymes and lysosomal enzymes, while the longer, more distal portion of the proximal tubule anlage develops into thin undifferentiated epithelium that is a transitory feature of the immature loop stage. The primitive epithelium of the distal tubule anlage develops into distal straight tubule epithelium. The cytologically sharp boundary of the thin undifferentiated epithelium and distal tubule epithelium is located just before the bend of the loop. The loop of Henle matures as the thin undifferentiated epithelium in the medullary ray and outer stripe of the outer medulla becomes transformed into proximal straight tubule epithelium. At the point where this descending differentiation ends, the borderline of the inner and outer stripe of the outer medulla arises. The thin undifferentiated epithelium in the inner stripe and the inner medulla differentiates into the thin epithelium of the descending limb of Henle's loop. In the bend and ascending limb of long loops, the thick distal tubule epithelium is trans-formed by an ascending autophagous process into the thin epithelium of the ascending limb of Henle. The termination of this process marks the borderline between the inner and outer medulla. The thin descending and thin ascending limb of Henle arise from 2 different anlages; between them lies the histogenetic boundary of the proximal and distal renal tubule.Supported by the Deutsche Forschungsgemeinschaft (SFB 105)     

Spermiogenesis and spermiation in a monotreme mammal, the platypus, Ornithorhynchus anatinus

Spermatogenesis in the platypus ( Ornithorhynchus anatinus ) is of considerable biological interest as the structure of its gametes more closely resemble that of reptiles and birds than marsupial or eutherian mammals. The ultrastructure of 16 steps of spermatid development is described and provides a basis for determining the kinetics of spermatogenesis. Steps 1–3 correspond to the Golgi phase of spermatid development, steps 4–8 correspond to the cap phase, steps 9–12 are the acrosomal phase, and steps 13–16 are the maturation phase. Acrosomal development follows the reptilian model and no acrosomal granule is formed. Most other features of spermiogenesis are similar to processes in reptiles and birds. However, some are unique to mammals. For example, a thin, lateral margin of the acrosome of platypus sperm expands over the nucleus as in other mammals, and more than in reptiles and birds. Also, a tubulobulbar complex develops around the spermatid head, a feature which appears to be unique to mammals. Further, during spermiation the residual body is released from the caudal end of the nucleus of platypus sperm leaving a cytoplasmic droplet located at the proximal end of the middle piece as in marsupial and eutherian mammals. Other features of spermiogenesis in platypus appear to be unique to monotremes. For example, nuclear condensation involves the formation of a layer of chromatin granules under the nucleolemma, and development of the fibrous sheath of the principal piece starts much later in the platypus than in birds or eutherian mammals.     

What Makes the Kidney Susceptible to Hypoxia?

Per gram of tissue, the kidneys are among our most highly perfused organs. Yet the renal cortex and, in particular, the renal medulla are susceptible to hypoxia. In turn, hypoxia is a major pathophysiological feature of both acute kidney injury and chronic kidney disease. We identify seven factors that render the kidney susceptible to hypoxia: (1) the large metabolic demand imposed by active reabsorption of sodium; (2) limitations on oxygen delivery to cortical tissue imposed by the density of peritubular capillaries; (3) the poor capacity for angiogenesis in the adult kidney; (4) the limited ability of the renal vasculature to dilate in response to hypoxia; (5) diffusive oxygen shunting between arteries and veins in the cortex and descending and ascending vasa recta in the medulla; (6) the physiological requirement for low medullary blood flow to facilitate urinary concentration; and (7) the topography of vascular-tubular arrangements in the outer medulla that limit oxygen delivery to the thick ascending limb of Henle's loop. Recent collaborative efforts between anatomists, physiologists, and mathematicians have improved our understanding of the roles of these factors in both physiological regulation of intrarenal oxygenation and development of renal hypoxia under pathophysiological conditions. We are also better able to understand these apparent maladaptations in the context of evolution. That is, they can be explained by the combined effects of historical contingency (our ancestral life in the sea) and selection pressures imposed by the multiple functions of the kidney to regulate extracellular fluid volume, retain water, and control erythrocyte production.     

Monoclonal antibodies against membrane proteins of the rat glomerulus. Immunochemical specificity and immunofluorescence distribution of the antigens.

Monoclonal antibodies (MAbs) were generated to detergent-solubilized glomerular extracts to identify new epithelial and endothelial membrane proteins and to study the possible role of the corresponding antigens in the formation of immune deposits. Triton X-114 extracts of isolated glomeruli were subjected to phase separation, and the resultant detergent and aqueous phases were used to immunize mice. Monoclonal antibodies were prepared by standard techniques, and hybridomas secreting antibodies (IgGs) that recognize glomerular cell surface antigens were selected by enzyme immunoassay (EIA) and indirect immunofluorescence. The IgGs of 13 MAbs selected for study recognized antigens of different molecular weights (45-350 kd) by immunoprecipitation and immunoblotting and had different distributions in the glomerulus and in other renal structures by immunofluorescence. Several proved to recognize known antigens--ie, podocalyxin (MAbs 1A, 5A, 11A, and 20A), gp330 (20B), and dipeptidylpeptidase IV (26C). Others recognized antigens not previously characterized that fell into four groups: 1) those that were detected mainly in glomeruli; 2) those present in both glomeruli and peritubular capillaries; 3) those present in both glomeruli and tubule epithelia; and 4) those detected in all these sites. The pattern of glomerular staining also varied, but most of the antigens appeared to be expressed on either the endothelium or the epithelium, or on both. 27A IgG was specific for podocytes and weakly precipitated a 103-kd protein. 7A and 13A IgG precipitated a 120-kd protein and stained glomeruli as well as the basal aspects of distal tubules. 23A IgG recognized a more-than 350-kd antigen that appeared to be specific for endothelial cells in rat kidney and in all other organs studied. 14A IgG precipitated a 150-kd protein and stained glomeruli, proximal tubule brush borders, and endothelial and epithelial cells in rat kidney and in several other organs. 4B and 9B IgG gave a granular cytoplasmic staining in all cells. When injected intravenously into rats, all of the MAbs except 4B and 9B rapidly bound to glomeruli, demonstrating that the respective antigens are exposed at the cell surface and represent potential targets for antibody-mediated immune injury. It is concluded that selective detergent extraction of glomeruli is a useful approach for generation of antibodies that recognize native, nondenatured membrane components of glomerular endothelial and epithelial cells.     

扬子鳄（Alligator sinensis）肾的超微结构

用透射电镜观察扬子鳄肾的超微结构。它的近曲小管和收集管上皮细胞无质膜内褶，远曲小管上皮细胞有较少的质膜内褶。扬子鳄肾小管的这些结构特征与它们在淡水生活有关。本文还就扬子鳄的栖息环境及其肾的超微结构与关咸水生活的美洲鳄进行了比较。     

Identification and characterization of membrane cofactor protein (CD46) in the human kidneys

Membrane cofactor protein (MCP, CD46) is an integral protein that serves as a cofactor for factor I in inactivating C3b/C4b deposited on the same cell-membrane as C3bi/C4c+C4d. This C3b/C4b inactivation is closely associated with self-protection of host cells from autologous complement attack. We have studied the distribution and properties of MCP in the normal human kidney by immunohistochemical and immunoblotting methods using monoclonal antibodies against MCP. MCP was predominantly expressed on the juxtaglomerular apparatus. Glomerular capillary walls, mesangial areas, and tubulus were also MCP positive. Glomerulus MCP was composed of two major bands of 45–65 kDa, which were similar to those of lymphocyte MCP. The proportion of the high and low molecular weight components in glomerulus MCP, however, was considerably different from that of lymphocyte MCP among the individual samples tested. Glomerular epithelial cells and mesangial cells from an individual having equal amounts of high and low molecular weight components in the lymphocytes were cultured seperately and the properties of their MCP investigated. MCP in the mesangial cells and glomerular epithelial cells showed profiles in which the upper band was predominant. The results may explain the unique distribution of the high and low molecular weight forms in the glomerulus. These forms of MCP together with factor I were all capable of inactivating C3b to C3bi. Message analysis suggested that glomerular epithelial cells and mesangial cells synthesized a single species of mRNA of 4.2 kb from which the polymorphic MCP species were generated. Flow cytometric analysis suggested that MCP was minimal in mesangial cells. These results, taken together with the previous reports on the distribution of other complement regulatory proteins, infer that the distribution profile of MCP is rather similar to that of DAF but differs from those of CD59 and CR1 in the normal human kidney; this may reflect the differences between their roles or functional properties in renal tissue.     

The pattern of distribution of selected ATP-sensitive P2 receptor subtypes in normal rat kidney: an immunohistological study

Using immunohistological techniques and available polyclonal antibodies, we have identified several ATP-sensitive P2 receptor subtypes in specific structures of the normal rat kidney. Of the P2 receptor subtypes examined, P2X1, P2X2 and P2Y1 receptors were found in the smooth muscle layer of intrarenal vessels. The P2Y1 receptor was also found on glomerular mesangial cells, the brush border membrane of the proximal straight tubule and on peritubular fibroblasts. In the cortex, P2Y4 receptors were found on the tubule epithelium of the proximal convoluted tubule, and P2Y2 receptors on glomerular epithelial cells (podocytes). P2X4 and P2X6 receptors were present throughout the renal tubule epithelium from the proximal tubule to the collecting duct. P2X5 receptors were expressed on medullary collecting duct cells and the apical membrane of the S3 segment of the proximal tubule. Possible functions of these receptor subtypes in normal rat kidney are discussed.     

破坏狗肾淋巴循环对移植肾影响的实验研究

目的：探讨自体肾移植后淋巴因素对移植肾的影响，为肾移植术是否需要吻合淋巴管提供参考。方法：实验动物为８只成年家犬，开腹，游离并切断左侧肾蒂，置于左髂窝，将肾动脉与左髂内动脉吻合，肾静脉与左髂总静脉吻合，但不吻合淋巴管，右肾作为对照，分别在术后第８、１２、２１天处死动物，用肉眼，光镜和透射电镜观察移植肾的变化。结果：肉眼观，左右肾的大小，颜色，质地无差别，但移植肾与周围组织广泛粘连；光镜：健侧肾皮质肾小管上皮细胞有水样变性，髓质内偶见少量的蛋白和细胞管型。患侧肾除见到与健侧类似的变化外，皮质内偶见脂肪变性，少数肾小球萎缩，部分肾小球代偿性肥大和集合管间质轻度纤维化；电镜：两侧肾小球无明显异常，实验侧近曲小管上皮细胞肿胀，微绒毛排列紊乱，胞浆内空泡增多，线粒体模糊，溶酶体增多，远曲小管和集合管部分上皮细胞坏死。结论：肾移植时可暂不考虑吻合淋巴管     

Immunofluorescent localization of Tamm-Horsfall mucoprotein in human kidney

A fluorescein-labelled antiserum to human Tamm-Horsfall mucoprotein applied to frozen human kidney sections gave strong specific labelling, mainly of cells of tubules in the outer medulla. By comparison with adjacent serial sections stained for alkaline phosphatase and succinic dehydrogenase, it is suggested that material reacting immunologically as Tamm-Horsfall muco-protein is found particularly in the cells of the ascending limb of the loop of Henle and the macula densa segment of the distal tubule.     

Heterogenous distribution of glycoconjugates in the kidney of dogfish Scyliorhinus caniculus (l.) with reference to changes in the glycosylation pattern during ontogenetic development of the nephron

Eight fluorochrome-coupled lectins with different sugar specificities were applied to cryosections of dogfish kidney. Despite profound differences in renal architecture between clasmobranch fish and other vertebrates, the sequence of nephron segments as revealed by the lectin-binding pattern was rather similar to that of tetrapodes. Wheat germ agglutinin (WGA) bound to cell membranes of epithelial cells of glomeruli, proximal and distal tubules, their basement membranes, the collecting tubule, and epithelial cells. Among other broadly binding lectins were Ricinus communis agglutinin I (RCA-I), soybean agglutinin (SBA), peanut agglutinin (PNA), Lycopersicon esculentum agglutinin (LEA), and Jacalin, all of which marked proximal as well as distal portions of the renal tubule. Dolichos biflorus agglutinin (DBA) did not react with any renal structure. Ulex europaeus agglutinin I (UEA-I), which indicates the presence of α-L-fucose, very strongly and specifically marked single epithelial cells of the early distal nephron, all epithelial cells of the late distal tubule, the beginning of the collecting tubule in the mesial tissue zone, and single cells in the end portion of the collecting tubule in the lateral bundles. Binding of UEA-I to receptors of distal nephron cells could be useful for the identification of these cells in functional studies employing teased tubule and/or isolated cell preparations. Binding of UEA-I to dogfish kidney structures resembles staining with UEA-I conjugates of late distal tubules and collecting tubules in the kidneys of frog and other, higher vertebrates. Epithelial cells of early developmental stages showed, very rarely, binding sites for most lectinfluorochrome conjugates. A large number of lectin binding sites was observed in the extracellular matrix of fibroblast layers surrounding the early anlage and the S-shaped body. Lectin binding sites of the nephron epithelia appeared in a sequential manner in the next stages of development of the nephron. Ontogenetic and phylogenetic aspects of the merging region between nephron proper (late distal tubule) and collecting system (collecting tubule) are discussed. © 1993 Wiley-Liss, Inc.     

Histological and immunohistological investigation of lymphoid tissue in the platypus (Ornithorhynchus anatinus)

The gross and histological appearance and the distribution of T and B lymphocytes and plasma cells are described for lymphoid tissues obtained from 15 platypuses. The spleen was bilobed and surrounded by a thick capsule of collagen, elastic fibres and little smooth muscle. White pulp was prominent and included germinal centres and periarterial lymphoid sheaths. Red pulp contained haematopoietic tissue. A thin lobulated thymus was located within the mediastinum overlying the heart. The cortex of lobules consisted of dense aggregates of small and medium lymphocytes, scattered macrophages and few reticular epithelial cells. In the medulla, Hassall's corpuscles were numerous, lymphocytes were small and less abundant, and reticular cells were more abundant than in the cortex. Lymphoid nodules scattered throughout loose connective tissue in cervical, pharyngeal, thoracic, mesenteric and pelvic sites measured 790±370 μm (mean±S.D. , n = 39) in diameter, the larger of which could be observed macroscopically. These consisted of single primary or secondary follicles supported by a framework of reticular fibres. Macrophages were common in the germinal centres. The platypus had a full range of gut-associated lymphoid tissue. No tonsils were observed macroscopically but histologically they consisted of submucosal follicles and intraepithelial lymphocytes. Peyer's patches were not observed macroscopically but histologically they consisted of several prominent submucosal secondary follicles in the antimesenteric wall of the intestine. Caecal lymphoid tissue consisted of numerous secondary follicles in the submucosa and densely packed lymphocytes in the lamina propria. Bronchus-associated lymphoid tissue was not observed macroscopically but was identified in 7 of 11 platypus lungs assessed histologically. Lymphoid cells were present as primary follicles associated with bronchi, as aggregates adjacent to blood vessels and as intraepithelial lymphocytes. The distribution of T lymphocytes, identified with antihuman CD3 and CD5, and B lymphocytes and plasma cells, identified with antihuman CD79a and CD79b and antiplatypus immunoglobulin, within lymphoid tissues in the platypus was similar to that described in therian mammals except for an apparent relative paucity of B lymphocytes. This study establishes that the platypus has a well-developed lymphoid system which is comparable in histological structure to that in therian mammals. It also confirms the distinctiveness of its peripheral lymphoid tissue, namely lymphoid nodules. Platypus lymphoid tissue has all the essential cell types, namely T and B lymphocytes and plasma cells, to mount an effective immune response against foreign antigens.     

Recent structure-function relationships in normal and injured mammalian kidneys

Recent investigations have been aimed at understanding the ultrastructural-functional relationships within the kidney at organ, tubule, subcellular, and molecular levels. This has led to a redefinition and more precise segmentation of the renal tubule. For example, the connecting piece between distal tubule and collecting system has now been established. The use of immunocytochemical techniques, such as fluorescence, ferritin- or peroxidase-labelled immunoglobulin methods, has made it possible to identify proteins in the kidney especially in renal corpuscles. Two major noncollagenous glycoproteins, fibronectin and laminin, have now been identified in the glomerulus. The glycosaminoglycan, heparan sulfate, has been localized to the glomerular basement membrane and is thought to play an important role in charge perm-selectivity during glomerular filtration. Subtle changes in glomerular podocyte or endothelial cell structure are postulated by some to play a role in the pathogenesis of acute renal failure. The role of the mesangial cell in glomerular function is being studied in situ in homogeneous cell populations. These cells are capable of prostaglandin production and can contract in response to hormonal stimulation. The intimate positioning of short- and long-looped nephrons in the renal medulla and the unique nature of the pelvic epithelium correlates well with the purported role of urea recycling in the urinary concentrating mechanism. Determination of elemental concentration of soluble substances in various renal cell and extracellular compartments have been made using freeze-hydrated and freeze-dried cryosections of kidney tissue. The medullary and cortical ascending thick limbs of the distal tubule are morphologically and functionally distinct regions. Their response to hormonal stimulation and their enzymatic activities are quite different. Morphological studies of the collecting duct have provided new insight into the role this segment of the uriniferous tubule plays in fluid and electrolyte transport and urinary acidification.     

Renal Na-K-ATPase Activity during Saline Infusion in the Rabbit

During saline infusion, sodium reabsorption (R_Na) in the diluting segment (thick ascending limb of Henle's loop) increases acutely. The mechanism for this higher pumping rate of outer medullary Na-K-ATPase is unknown. Following left-sided nephrectomy, immediate i.v. infusion of hypertonic saline increased R_Na in the remaining whole right kidney by 28 ± 14% (p < 0.05). Na-K-ATPase activity in outer medulla was raised by (A) 23 + 4% above the left kidney (p < 0.05), whereas cortical activity was unchanged. The mechanism for this increase in Na-K-ATPase activity was explored. The catalytic rate per enzyme did not differ in the two kidneys and equalled 5 340 min^-1. The increase was therefore due to higher tissue concentration of active enzyme. The response was fully developed during continuous infusion within 20 min, and of equal magnitude whether protein synthesis had been inhibited by cycloheximide (Δ= 23 ± 7%) or stimulated by unilateral nephrectomy 6 days earlier combined with saline infusion for 2 h (Δ= 34+ 10 %). Thus, during hypertonic saline infusion, the increased R_Na in the outer medulla was partly accounted for by the activation of latent Na-K-ATPase. High delivery of sodium to the diluting segment for more than 20 min during hypertrophy caused no further activity change.     

Malignant synovioma: electron microscopical findings in three patients and review of the literature.

Ultrastructural findings in three malignant synoviomas are described. Two typical "biphasic" tumours contained "epithelial" cells possessing filopodia or microvilli, specialised cell attachment and a basal lamina, and smaller "stromal" cells showing transitions to fibroblasts. In one case, the microvilli included fibrils resembling those in epithelial cells of the intestine and renal tubules. The third tumour was mainly spindle-celled with little epithelial differentiation and no clear division into cell types, but intracytoplasmic microfibrils were conspicuous, forming ovoid masses. The tumour cells differ a good deal from normal human synovial cells but some of the features of the neoplasm are found in inflamed human synovium and in normal synovial membranes of other species. The cytoplasmic fibrils in the third case are similar to those reported by others in epithelioid sarcoma, a tumour that may be of related origin to synovioma; however, the phenomenon may be merely degenerative.