An Electron Microscopic Study of the Ductuli Efferentes and Rete Testis of the Guinea Pig

Morphological and ultrastructural study of the efferent ductules in the Chinese soft-shelled turtle Pelodiscus sinensis

Comparative study of the turtle excurrent duct system increases our understanding the evolution of sperm motility and fertility maintenance in higher vertebrates. Therefore, in this study we observed the histology and ultrastructure organization of efferent ductules in the Pelodiscus sinensis using light and transmission electron microscopy. The efferent ductules are extra- testicular and 22-28 in number originate from rete testis. The epithelium is entirely composed of two types of cells, the predominant non-ciliated and ciliated cells. The ciliated cells have long cilia that protrude into the lumen to form a meshwork. These cells associated with clusters of mitochondria in the supranuclear cytoplasm and possess coated vesicles, vacuole, intracellular spaces, and junction complexes. Ciliated cells in the proximal portion of the ductules contain an endocytic apparatus with coated pits and tubules in the apical cytoplasm. Interdigitations and lipid droplets are predominantly present around the nuclei of these cells. The non-ciliated cells have clusters of mitochondria present in both the supranuclear and perinuclear cytoplasm whereas, the nuclei of these cells are lightly stained. Moreover, the contour of the epithelium towards lumen is irregular as it has a deep indentation. The apical cytoplasm goes deep into the lumen to form cytoplasmic processes. This is the first study to describe the detailed features of efferent ductules in Pelodiscus sinensis with, special focus on the morphology of ciliated cells, as these cells are involved in the mixing of luminal fluid and transport of spermatozoa towards the distal region.

A.J. Ladman: managing editor of The Anatomical Record, 1968-1998

In the period 1906-1998, The Anatomical Record has had only six managing editors. One of these individuals, A.J. Ladman, served in this capacity for 30 years, almost a full third of the history of this journal up to 1998. Ladman received his Ph.D. degree from Indiana University in 1952, was at Harvard for 9 years (1952-1961) and at the University of Tennessee from 1961-1964. He became professor and chairman of the Department of Anatomy at the University of New Mexico School of Medicine in 1964. In April 1968, Ladman was appointed managing editor of The Anatomical Record by the American Association of Anatomists (AAA). He brought energy and innovative ideas to the journal and would apply those in the changes he instituted over the years of his tenure. In April 1998, after 30 years of exemplary service to this journal and to the AAA, Ladman passed the responsibility on to Roger Markwald. During his career, and in addition to his editor's work, he conducted research on an impressively wide range of topics, served as an elected officer in several professional organizations, and was founding chair of anatomy at New Mexico. He went to Hahnemann in 1981, served as Dean of the School of Allied Health Professions (1981-1986), and is currently adjunct professor of neurobiology and anatomy. The AAA expresses its sincere appreciation to A.J. Ladman for his excellent stewardship of The Anatominal Reord.

The fine structure of the epithelial lining of the epididymis of the camel (Camelus dromedarius) with special reference to regional differences

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Role of apical tubules in endocytosis in nonciliated cells of the ductuli efferentes of the rat: a kinetic analysis

The apical region of nonciliated cells of the ductuli efferentes of the rat contains tubular coated pits (TCP) connected to the apical plasma membrane, apical tubules (AT) which occasionally show a partial coat, and endosomes which are often continuous with one or more apical tubules. To investigate the formation and fate of TCP and AT, a quantitative analysis was performed on the labeling indices of these structures at various time intervals (0.5-120 min) after a single injection of a tracer, cationic ferritin (CF), into the lumen of the rete testis. The labeling indices of both TCP and AT exhibited similar cyclical patterns, first reaching a peak at 25 min, then dropping to a minimum at 35 min, then rising to a second peak at 60 min. Since TCP were well labeled at 30 sec while AT were not, the tracer must rapidly enter TCP and thence AT. However, since tracer was virtually absent from the lumen by 30 min, it was not possible to reconcile the second peak of labeling index of TCP and AT by this mechanism. In another experiment, rats were injected once as before, injected again at 30 min, and then sacrificed at 30 min following the second injection. The results from this experiment showed that the labeling index of TCP and AT did not drop but was similar to that of the 60-min peak after a single injection. The interpretation is that there was recycling of tracer, which had already migrated from TCP to AT to endosomes, back to the apical plasma membrane via apical tubules. Moreover, when rats were injected once, injected again at 30 min, and sacrificed 3 min following the second injection, the labeling index for TCP and AT was significantly higher (P less than .05) than at the 30-min time interval after a single injection, indicating that recycled apical tubules were functionally capable of binding further CF. Morphological observations on images of transition between TCP and AT and the fact that AT were often found connected to endosomes suggest that TCP detach from the cell surface to give rise to AT, which in turn fuse to form endosomes. The kinetic analysis demonstrates in quantitative terms that a portion of the AT, which fuses to form endosomes, recycles back to the apical plasma membrane and contributes to the formation of new TCP.

Helical structure in the apical tubules of several absorbing epithelia. Kidney proximal tubule, visceral yolk sac and ductuli efferentes

Unique and highly ordered structures were discovered in the so-called apical tubules of several absorbing epithelia (kidney proximal tubule, visceral yolk sac and ductuli efferentes) fixed in situ with a mixture of formaldehyde, glutaraldehyde and osmium tetroxide. The apical tubules were especially numerous in the apical cytoplasm, in addition to the invaginations of the apical plasma membrane, newly formed endocytic vesicles and large endocytic vacuoles. They showed a cylindrical structure (approximately 80 nm in diameter) limited by a smooth membrane. Helically wound parallel rows of particles (approximately 11 nm in diameter) were found in the apical tubules in close proximity to their limiting membrane. The structure of the helix was determined by following the rows through serial sections and semithin sections, and was found to be a left-handed quadruple helix. These particles surround an electron-lucent cylinder (approximately 35 nm in diameter), containing at its center a single row of particles (approximately 9 nm in diameter). The apical tubules with the luminal specializations were not seen in continuity with the apical plasma membrane, but were frequently connected with the large endocytic vacuoles, which were present in the deeper levels of the apical cytoplasm. From these observations, it is suggested that the apical tubules are not derivatives of the apical plasma membrane; rather, they represent an intracellular compartment, which is morphologically related to the large endocytic vacuoles.

The ultrastructure of the epithelium of the ductuli efferentes testis in the common starling (Sturnus vulgaris)

The ductuli efferentes of male common starlings (Sturnus vulgaris) were prepared for light and electron microscopy. The epithelium of breeding birds was pseudostratified, consisting of ciliated cells, which were of the same type throughout the ductules, and of two types of non-ciliated cells: an electron-dense form with complex lateral invaginations, long microvilli and apical invaginations found in proximal ductuli efferentes (Type 1 a) and a less dense, taller, seemingly more secretory cell found distally (Type 1 b). Both types contained crystal-like structures in granular and transitional endoplasmic reticulum, which were occasionally seen in ciliated cells and not elsewhere. These 'intracisternal bodies' were probably proteinaceous in nature. The ciliated cells were typically more electron-lucent than the non-ciliated cells. They adopted the height and interdigitation characteristics of the surrounding epithelium. Occasional annulate lamellae were encountered. Intraepithelial lymphocytes were seen occasionally, notably in non-breeding birds. The epithelial morphology of the non-breeding common starling is briefly mentioned. The tubules were collapsed and apparently inactive, although signs of proliferative activity were seen in birds killed in February. The distinction of the epithelial cells into one ciliated and two non-ciliated types in this study is discussed in the light of previous work, as differences were found to exist. It is suggested that care should be taken in the use of mammalian tubule nomenclature when it is applied to birds.

Fluid-phase and adsorptive endocytosis in ciliated epithelial cells of the rat ductuli efferentes

Ciliated cells of the ductuli efferentes show at their apex a discrete endocytic apparatus composed of small vesicles connected to or subjacent to the apical plasma membrane, small apical membranous tubules, and pale multivesicular bodies. Deeper in the cytoplasm, there are acid phosphatase-positive denser, multivesicular bodies and secondary lysosomes showing an electron-dense cortex and a crystalline, paler stained core. Cationic ferritin and concanavalin A-ferritin used to demonstrate adsorptive endocytosis, when injected into the rete testis, rapidly reached the lumen of the ductuli efferentes. At 1 min after injection, these tracers were seen bound to the apical plasma membrane of ciliated cells and within small endocytic vesicles and by 5 min in narrow apical tubules. At 15 and 30 min after injection, the tracers appeared in pale multivesicular bodies while at 1 hr they were found within dense multivesicular bodies. At 2 hr and longer time intervals these tracers accumulated within secondary lysosomes. Native ferritin, concanavalin A-ferritin in the presence of alpha-methyl-D-mannoside, and horseradish peroxidase or albumin-colloidal gold complexes were used to analyze fluid-phase endocytosis. At various intervals following their injection into the rete testis, these tracers presented a distribution identical in all respects to that described for cationic ferritin and concanavalin A-ferritin. In the present work, none of the above tracers were transported to the abluminal aspect of the ciliated cells. These cells, like the nonciliated epithelial cells of the ductuli efferentes are thus involved in adsorptive as well as in fluid-phase endocytosis.

Endocytosis in nonciliated epithelial cells of the ductuli efferentes in the rat

The nonciliated cells lining the ductuli efferentes presented three distinct cytoplasmic regions. The apical region contained, in addition to cisternae of endoplasmic reticulum and mitochondria, two distinct membranous elements. The tubulovesicular system consisted of dilated tubules connected to the apical plasma membrane and subjacent distended vesicular profiles. The apical tubules, not connected to the cell surface, consisted of numerous densely stained tubules of small size which contain a compact, finely granulated material. The supranuclear region, in addition to a Golgi apparatus and ER cisternae, contained dilated vacuoles, pale and dense multivesicular bodies, as well as numerous dense granules identified cytochemically as lysosomes. The basal region contained the nucleus and many lipid droplets. The endocytic activity of these cells was investigated using cationic ferritin (CF) and concanavalin-A-ferritin (Con-A-ferritin) as markers of adsorptive endocytosis; and native ferritin (NF), concanavalin-A-ferritin in the presence of alpha-methyl mannoside, and horseradish peroxidase or albumin bound to colloidal gold for demonstrating fluid-phase endocytosis. These tracers were injected separately into the rete testis, and animals were sacrificed at various time intervals after injection. At 1 min, CF or Con-A-ferritin were seen bound to the apical plasma membrane, to the membrane of microvilli, and to the membrane delimiting elements of the tubulovesicular system. Between 2 and 5 min, these tracers accumulated in the densely stained apical tubules and at 15 min in the dilated vacuoles. Between 30 min and 1 hr, the tracers appeared in multivesicular bodies of progressively increasing density, whereas at 2 hr and later time intervals, many dense lysosomal elements became labeled. The tracers for fluid-phase endocytosis showed a distribution similar to that for CF or Con-A-ferritin except that they did not bind to the apical plasma membrane, microvilli, or membrane delimiting the tubulovesicular system. At no time interval were any of the tracers observed in the abluminal spaces. Thus, the nonciliated epithelial cells of the ductuli efferentes are actively involved in fluid-phase and adsorptive endocytosis, both of which result in the sequestration of endocytosed material within the lysosomal apparatus of the cell.

Seasonal changes in fine structure of the ductuli efferentes of the ground squirrel, Citellus lateralis (Say)

The morphological changes that the ductuli efferentes undergo during the seasonal breeding cycle of the ground squirrel Citellus lateralis were examined by means of electron microscopy. At the time of spermatogenetic activity the epithelium of the ductuli was composed of highly differentiated principal and ciliated cells. Distinctive cytological features of these cells during this period were the presence of a heterogeneous collection of numerous membrane-bound granules in principal cells and large accumulations of glycogen in ciliated cells. Structurally these cells were specialized for movement of luminal contents and its modification by absorption and possible secretion. With the onset of testicular regression, profound changes occurred in both cell types. Initially the lumen of the ductuli became occluded by masses of apical cytoplasm protruded from principal and ciliated cells as well as by degenerating cells which had been sloughed from the epithelium. This leads eventually, by the time of complete testicular regression, to reduced ductuli containing cells smaller in size with fewer organelles than those present during the period of spermatogenesis. The membrane-bound granules in principal cells and the accretions of glycogen in ciliated cells had now virtually disappeared. There was, however, a dramatic increase in dense inclusions representing deposits of lipofuchsin. As yet the cellular mechanisms controlling and effecting these dramatic changes in morphological appearance are unknown.

Demonstration of fluid-phase endocytosis in epithelial cells of the male reproductive system by means of horseradish peroxidase-colloidal gold complex

The occurrence of fluid-phase endocytosis in Sertoli cells as well as epithelial cells of the rete testis and ductuli efferentes was demonstrated by use of horseradish peroxidase combined with colloidal gold (HRP-G) as a tracer. The characteristic electron dense spherical colloidal gold particles facilitate the localization of the HRP-G complex in pinocytotic vesicles, multivesicular bodies, and lysosomes of these epithelial cells. With this method, which does not require the use of diaminobenzidine, a clear distinction can be made between peroxidases from endogenous and exogenous origins.

The rete testis of birds

The rete testis in the domestic fowl (Gallus gallus domesticus), Japanese quail (Coturnix coturnix japonica), guinea-fowl (Numida meleagris galeata) and drake (Anas platyrhynchos) was studied histologically and with both the scanning and transmission electron microscopes. All the birds have rete epithelial cells varying between squamous and high cuboidal. A cilium-like structure projects from the luminal portion of most cells into the rete lumen, and the outline of the cells varies from polygonal to elongate. Sparse, stubby microvilli were concentrated on the cell borders. Ultrastructural features suggest only moderate secretory and absorptive activities in the cells. The rete testis of birds is amply supplied with blood as well as lymphatic vessels and nerves. Intraepithelial lymphocytes form part of the rete epithelium, and macrophages are present in large numbers in the rete lumen of the domestic fowl and drake and, to a lesser degree, also in the rete epithelium of the drake.

Microvasculature of the mouse testis and excurrent duct system

The microvascular architecture of the mouse testis and excurrent duct system was examined by a casting method with the aid of scanning electron microscopy and by sectioning techniques for light and transmission electron microscopy. Two fundamental types of peritubular capillary arrangements were noted in relation to the tubules. The first type most typically appeared in the testis. In this type, peritubular capillaries interconnected intertubular blood vessels to form a rope-ladder-like structure. The length of the individual peritubular capillaries was short, and a number of the capillaries encircled each tubule. Adjacent tubules shared a single layer of capillaries. The vascular organization of the ductuli efferentes and of the middle segment of the epididymis was also of this type, but the number of peritubular capillaries was much fewer compared with that of the testis. In the second type, the peritubular capillaries formed a network encircling each tubule in its subepithelial layer. The capillary organization in the initial and terminal segments of the epididymis and the ductus deferens belonged to the second type. In the distal part of the ductus deferens, a prominent venous plexus was formed in the most peripheral subepithelial layer.

Sertoli cell and sertoli-Leydig cell tumors of the ovary. A report of three cases with ultrastructural findings

Three tumors of the ovary containing Sertoli cells were studied by light and electron microscopy. Two of these tumors were well-differentiated neoplasms with epithelial cells often forming tubules. These cells were cylindrically shaped, contained round to oval nuclei and stood on a thin basement membrane. The cytoplasm was fibrillary and showed rough and smooth endoplasmic reticulum, lipid droplets and secretory granules. At the luminal borders the cells were often irregular and displayed apocrine-like activity. Having compared our data with results of studies from the literature of normal Sertoli cells, Sertoli cell adenomas of the testis and cells from other parts of the male reproductive system and those of normal ovarian stroma, we conclude that the Sertoli cell is most probably the cell of origin of these tumors. The third tumor was undifferentiated with a sarcomatoid appearance and contained islands of cartilage, which we consider to be metaplastic.

Clear cell adenocarcinoma of the female urethra: clinical and ultrastructural study suggesting a unique neoplasm

A case of clear cell adenocarcinoma arising in the female urethra is described. The tumor had a tubulocystic pattern and intracytoplasmic glycogen, resembling clear cell carcinomas that occur in the vagina and upper female genital tract. Ultrastructural study, however, showed abundant and elongated microvilli on the tumor cells, a feature not seen in clear cell carcinomas or other common forms of carcinoma arising in the female genital tract. Six other cases of similar tumors of the female urethra were found in medical literature, yet there was no example of this tumor in the bladder or male urethra. Clinical and ultrastructural observations suggest that clear cell carcinoma of the female urethra is a distinctive neoplasm. Abundant microvilli provide morphologic evidence supporting the possibility of origin from the mesonephros. Radical extirpative surgery with urinary diversion appears to be the treatment of choice.

Studies of the deferent ducts from the testis of the African elephant, Loxodonta africana. III. Ultrastructure and cytochemistry of the ductuli efferentes

The epithelium of the ductuli efferentes is composed of ciliated, principal, halo and basal cells. The supranuclear cytoplasm of ciliated cells is penetrated by particularly long cilial rootlets which are surrounded by numerous elongate mitochondria. Microtubules are arranged along the longitudinal axis of the cells. The spaces between the microvilli of principal cells form canaliculi which penetrate the apical cytoplasm and appear to be involved in endocytotic activity. The supranuclear cytoplasm contains oval mitochondria and numerous vacuoles. Both ciliated and principal cells contain poorly developed Golgi and endoplasmic reticulum, but numerous supranuclear dense bodies are usually present. Supranuclear and basal accumulations of dense bodies were identified as lipofuscin; they were the source of brown pigmentation in the proximal two thirds of the ductuli efferentes. The halo cells were probably macrophages. They occurred quite frequently and contained crescent shaped nuclei and large accumulations of lipofuscin material.

Studies of the deferent ducts from the testis of the African elephant, Loxodonta africana. I. Structural differentiation

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Structural differentiation of the male genital ducts of the echidna (Tachyglossus aculeatus)

Seven ductuli efferentes radiate from the testis of the echidna and join the ductus epididymidis either directly or after joining one of their neighbours. They are pigmented brown and appear to be structurally and functionally similar to the ductuli efferentes of therian mammals. The epididymis is anatomically differentiated into a large head and small tail which appear to be, respectively, larger and smaller than the similar regions of the epididymis of scrotal mammals; they also contain, respectively, larger and smaller proportions of the animals' extragonadal spermatozoa. Only the head of the epididymis is adjacent to the testis: the tail and the ductus deferens are distal to the testis. The ductus epididymis is also histologically differentiated into two segments (initial and terminal segments) which correspond precisely with the anatomical differentiation. The initial segment is structurally similar to the initial segment of the epididymis of scrotal mammals (i.e. tall epithelium with long stereocilia, a farily homogeneous supranuclear cytoplasma containing Golgi apparatus and a low concentration of spermatozoa in the lumen). The terminal segment has adaptations of the duct (as in scrotal mammals) for the storage of spermatozoa such as a wide lumen containing a high concentration of spermatozoa, low epithelium and thick layers of periductal muscle. However, it is peculiar in that the duct epithelium is thrown into folds and it is involved in considerable apocrine secretion.

The resorptive activity in the bull efferent ductules--a morphological and experimental study

The resorptive activity of the efferent ductules was studied in mature and immature bulls using histochemical, electron microscopical, and experimental methods. Resorptive activity was indicated by the uptake of the protein tracer (HRP) and the presence of microvilli, endocytotic apparatus, and alkaline phosphatase activity. The above features were found in all three types of nonciliated cells, but were apparently best developed in vacuolated (type III) cells. The resorptive apparatus was fully developed by 25 weeks, an age which roughly corresponds with the luminization of seminiferous tubules and the onset of spermatogenesis. In mature bulls the resorptive apparatus was markedly affected by androgen deprivation resulting from orchidectomy and was restored by the administration of testosterone, indicating its dependence upon the circulating androgen. Efferentiectomy had little impact, indicating that the luminal androgen does not play a major role in maintaining the resorptive apparatus. The tracer study revealed that the specific granules and vacuoles of type II and III cells, respectively, are not associated with resorptive function. It also showed that the tracer injected into the rete testis took 6 to 24 hours to pass through the efferent ductules and reach the initial segment of the epididymis.

The ductuli efferentes of the epididymal region of birds

Ultrastructural studies were undertaken on the efferent ductules of the testis of the domestic fowl (Gallus domesticus), Japanese quail (Coturnix coturnix japonica) and guinea-fowl (Numida meleagris). Four cell types were identified and described: ciliated cells which were found in the epithelium of both the proximal and distal segments of the efferent ductules, non-ciliated Type I cell which, together with the ciliated cell, formed the epithelium of the proximal efferent ductule and the non-ciliated Type II cell which, together with the ciliated cell, formed the epithelium of the distal efferent ductule. Intraepithelial lymphocytes were the fourth cell type found in the epithelium of both segments of the efferent ductule of the fowl only.

The structure of the excurrent ducts of the testis of the guinea-fowl (Numida meleagris)

The epididymal region of the guinea-fowl was studied in sexually mature birds. The structure of the epididymal region was generally similar to that already described for the domestic fowl, turkey and Japanese quail. Well formed, intratesticular tubuli recti was seen connecting the seminiferous tubules with the rete testis. The latter consists of both intracapsular and extracapsular portions. Six main cell types were recognised in the region: the rete testis was lined by squamous cells, the proximal efferent ductules by ciliated and non-ciliated Type I cells, the distal efferent ductule by ciliated and non-ciliated Type II cells, and the connecting ductules, ductus epididymidis and ductus deferens were lined by non-ciliated Type III and basal cells. The cell classification adopted in this study is discussed.

The structure of the epididymis, efferent ductules and ductus deferens of the guinea pig: a light microscope study

In the guinea pig, the narrow part of the epididymis that traverses the upper pole of the testis and passes downward over the entire length of the gonad is composed exclusively of efferent ductules and the initial segment (zone I) of the epididymal duct. At the beginning of zone II, the narrow contour of zone I expands into a large globular region which lies adjacent to the caudal pole of the testis. The globular region of the guinea pig epididymis is commonly referred to as the cauda epididymidis but in the present study, examination with the light microscope reveals that it is composed of five histologically distinct zones (zones III through VII). A detailed histological analysis of the characteristics of the epithelium in the seven zones of the guinea pig epididymis and in the efferent ductules and ductus deferens was udertaken to obtain a better understanding of structure-function relationships in the epididymis of the guinea pig. It was found that each of the zones could be readily distinguished on the basis of its histological features and primarily on the basis of the appearance of the principal cells.

The mammalian rete testis--a morphological examination

The fine structure of the rete testis was examined in several primates, domestic animals and rodents. The rete testis consists of a series of interconnected wide channels lined with a simple cuboidal to columnar epithelium, resting on a thick basal lamina. Beneath the basal lamina dense bundles of collagen fibrils and a few blood vessels, lymphatics or nerve tissue are found. The epithelial cells are characterized by large, deeply indented nuclei, spherical or short rod-shaped mitochondria, supranuclear Golgi profiles, some cisterns of rough endoplasmic reticulum, free ribosomes and numerous micropinocytotic vesicles in the ectoplasmic regions. Smooth endoplasmic reticulum, secretory granules, lysosomes or other types of dense bodies are rarely seen. The apical surface of the cells bears numerous microvilli and a single very long flagellum which is presumed to be motile. Ajoining lateral cell membranes exhibit a juxtaluminal tight junction, elaborate interdigitations and desmosomes. The basal plasma membrane is highly irregular greatly increasing its surface area of contact with the underlying interstitium. The nuclei of the rete epithelial cells contain pale-staining, spherical structure, 2 mum in diameter, composed of circularly oriented fine filaments. The significance of the nuclear structures remains unknown. Thorotrast was injected into the lumen of the hamster and rat rete testis and 30 minutes later the proximal portion of the excurrent duct system of the testis was prepared for electron microscopy. Whereas the ductuli efferentes and first part of the epididymis possessed numerous apical vesicles filled with the thorotrast, this electron opaque substance was rarely found in the epithelium of the rete testis. Thus, incorporation of particulate matter into the lining cells of the rete from its lumen is apparently less active than in the epithelium of the ductuli and epididymis. Vascularly introduced intercellular tracer compounds such as lanthanum nitrate or horseradish peroxidase did not enter the lumen of the rete testis from the interstitium. The tracer molecules appeared to be blocked by the juxtaluminal tight junction separating adjacent epithelial cells. This latter observation suggests that a blood-testis barrier exists at the level of the rete testis epithelium. Although physiological studies have indicated that the composition of fluid secreted in the seminiferous epithelium is considerably modified in the rete testis, the present morphological study does not provide additional evidence to support a secretory or absorptive function for this region of the excurrent duct system of the testis.

The rete testis in man: ultrastructural aspects

The ultrastructure of the normal human rete testis was analyzed. The rete testis cavities are irregularly shaped and contain virtually no spermatozoa. Smooth muscle cells often surround the cavities. In the epithelial lining, two cell types are distinguishable. Flat, dark cells exhibit numerous slender microvilli, and numerous apical and basal micro-vesicles. Prismatic, lighter cells have more cell organelles, mostly polarized towards a supranuclear position. Both cell types contain variable amounts of glycogen and fat, and an occasional cilium. All cells display intricate lateral cell surfaces that possess different cell-to-cell attachment devices. Intermediate cell types are frequently found. On a morphological basis, the epithelial cells seem to be involved in the release of substances into the lumen and probably also in transport towards the base. Connective tissue elements are found subjacent to the epithelium. Scattered among the fibrocytes are typical smooth muscle cells. Expansions of some smooth muscle cells are connected to the epithelial basement membrane by a network of microfibrillar materia. The smooth muscle cells may be involved in changing the shape of the rete testis channels, thus promoting the flux of the rete testis fluid. Different types of nerve fibre bundles are distinguished in the connective tissue of the rete testis which may correspond to autonomic and sensory nerves or sensory receptors.

The ultrastructure of Leydig cells in the testis of the domestic fowl

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