The placenta of the pig. I. Finestructural changes of the placental barrier during pregnancy

The finestructural changes of the interareolar porcine placenta during pregnancy are described. After perfusion fixation of the placenta the change in the thickness of the placental barrier from day 30 to day 110 of gestation is much more evident than after immerson fixation as has been used by all former authors. The alterations are due to the indentation of both the trophoblast and uterine epithelium by their corresponding capillary-network. This indentation is limited to the lateral wall and the summit of the chorionic ridges, while at the base the trophoblast as well as the uterine epithelium remains high columnar. This indicates that in the interareolar porcine placenta, which is represented by the chorionic ridges and the corresponding endometrial folds, at least two different areas with different structure and function may be discerned. 1) The lateral side and the top of the chorionic ridges seem to be predestinated for gaseous exchange. The placental barrier in this area is often less than 2 micrometers. 2) The transport of blood-borne nutrients takes place at the base of the chorionic ridges. This transport seems to be facilitated by an intercellular channel system between the uterine epithelial cells.

Evidence for a fucose-binding protein in boar spermatozoa

A fucose binding protein was detected in boar spermatozoa by means of a specifically developed modified enzyme-linked-lectin-assay using glycosylated peroxidase derivatives. The distribution of the fucose binding protein was assessed by means of fluorescence microscopy with fluoresceinyl-glycosylated peroxidase. Fucose binding was particularly prominent at the apical region of the sperm head. In order to gain more insight into the precise localization of the carbohydrate binding protein electron microscopical studies were performed using fucosyl peroxidase coupled to colloidal gold. In ultrathin sections as well as in specimens prepared in toto for TEM an intensive binding of fucosylperoxidase-colloidal gold was predominantly found at the apical part of the acrosome appearing as a crescent-like area. In some cases this binding pattern was replaced by a triangle-like intensive labelling at the equatorial segment as revealed clearly by specimens prepared in toto. By SDS-PAGE of the SDS-extractable sperm-proteins, followed by transblotting to nitrocellulose and visualization with the fucosylperoxidase by enzymatic amplification with 4-chloro-1-naphthol mainly one protein with the reduced molecular weight of approximately 53 kdal and some small proteins with apparent molecular weights less than 20 kdal was found to be responsible for the fucose-binding ability of porcine spermatozoa.

The placenta of the pig. II. The ultrastructure of the areolae

The ultrastructure of the areolae in the porcine placenta is described. The areolae occur on day 30 of pregnancy as dome-shaped formation over the openings of the uterine glands. The lumen of the areolae is filled with the secretions of the uterine glands, the so-called histiotroph. The areolae lining epithelium is high collumnar, possessing long microvilli, a well-developed apical tubular system and numerous coated vesicles. This indicates that the epithelium has a high absorptive capacity. Our histochemical investigations reveal a high content of glycoproteins within the areolar lumen. The importance of one of the glycoprotein components of the histiotroph, uteroferrin, is discussed in connection with iron transfer from mother to the fetus.

Interdigitating reticulum cells in the popliteal lymph node of the rat. An ultrastructural and cytochemical study

Electronmicroscopic and cytochemical studies were performed to localize interdigitating reticulum cells (IDC) in the popliteal lymph node of the rat. The morphological features of the IDC of the rat correspond to those described for other species, but also show similarities to normal macrophages in the rat. This is considered to be an argument in favour of the common origin of IDC's and macrophages. Ultrahistochemical studies with horseradish peroxidase (HRP) reveal no phagocytotic capacity of IDC's. After perfusion fixation containing ruthenium red (RR) the surface coat stains heavily: RR is also found deep in the membrane invaginations of the IDC, indicating the presence of polyanionic sialoglycoproteins. The post-capillary-venules (PVC) are very permeable to both HRP and RR. The phosphotungstic acid-chromic acid stain (PTA-CrA) also reveals glycoproteins in the surface coat; these glycoproteins are susceptible to alpha-neuraminidase, whereas glycoproteins in the Golgi complexes, lysosomes and in the vesicular complexes of IDC are not. The glycoproteins of the latter are susceptible to 0.1 N NaOH. These findings indicate that IDC produce different kinds of glycoprotein, one of which may be secreted and act as a factor for stimulating peripheral T-lymphocytes. Intimate contact between IDC's and PCV's could be observed. It is therefore conceivable that IDC's play an important role in the homing of T-lymphocytes.

Uterine glands of the pig during pregnancy. An ultrastructural and cytochemical study

The ultrastructure of the porcine uterine glands is described from material taken from 11 pregnant pigs at exactly known stages of gestation (day 30; 58; 80; 100; 110). Fixation was performed by perfusion via a branch of the uterine artery and the tissue was routinely processed for electron microscopy. Additionally, cytochemical studies (phosphotungstic acid reaction for glycoproteins, according to Rambourg 1967; acid phosphatase reaction; ultrastructural localization of cellular iron, according to Parmley et al. 1978) were performed. On day 30 of pregnancy the uterine glands are coiled, simple tubular glands with a narrow lumen. The epithelial lining is simple columnar and consists basically of two cell types, ciliated cells and secretory cells. The secretory activity of the glandular epithelium is low; only a few secretory granules are present in the supranuclear cytoplasm. At midpregnancy the ultrastructure of the glands has significantly changed and the cells now show all the characteristics of high secretory activity: numerous parallel cisternae of rough endoplasmic reticulum, an extensively developed Golgi apparatus and many secretory granules which give a positive reaction for acid phosphatase and glycoproteins. The lumina of the glands are significantly enlarged and filled with a great amount of a granular, acid phosphatase-positive material. In the last third of pregnancy, only minor changes in the ultrastructure of the uterine glands are observed. The secretory activity is still high. The amount of rough endoplasmic reticulum has further increased and parallel arrays of cisternae occupy a considerable part of the supranuclear cytoplasm. The importance of the uterine secretion for embryonic nutrition and development is only partly understood. One of the secreted glycoproteins, uteroferrin, is believed to play an important role in the iron transfer from mother to fetus. From midpregnancy onward, a special cell type, the "granule laden cell" is found scattered between normal secretory cells of the uterine glands. Contrary to the opinion of Perry and Cromby (1982), we could demonstrate that these cells frequently extend to the lumen of the gland; hence the term "basal cell" seems inappropriate for this cell type.

The uterovaginal sperm host glands of the quail (Coturnix coturnix japonica): an ultrastructural and ultracytochemical study

Ultrastructural and ultrahistochemical studies were performed on the uterovaginal sperm host glands of the quail (Coturnix coturnix japonica). The proximal parts of the glandular necks are lined by a pseudostratified epithelium, consisting of high columnar ciliated cells and small, irregular shaped, basal cells. The true glandular epithelium is composed only of columnar cells with microvilli on their luminal end. A characteristic luminal feature is a large lipid droplet in the perinuclear region. In the subplasmalemmal region numberous tubular profiles are seen which could represent a cellular resorption system. To evaluate the absorptive capacity of the uterovaginal sperm host glands, tracer studies with HRP, ferritin, lanthanum and ruthenium red were undertaken. Since between 5 min and 3 h after injection no absorption could be found with the techniques mentioned, it is suggested that phagocytosis of spermatozoa by the glandular epithelium is not likely to occur.

Localization of lectin receptors on bovine epididymal spermatozoa using a colloidal gold technique

Mammalian spermatozoa that leave the testis are neither motile nor fertile. Maturation of spermatozoa occurs during epididymal transport. Among the changes during epididymal passage alterations of the surface properties of spermatozoa appear especially interesting. In this report we describe ultrastructural localization of Con A and WGA-binding sites on bovine spermatozoa from caput and cauda epididymides using a indirect lectin-horse-radish-peroxidase gold technique. With Con A the plasma-membrane covering the sperm head was heavily labelled with gold granules in caput as well as in cauda epididymal spermatozoa. A different distribution was observed for WGA-binding sites. The acrosomal region of caput and cauda spermatozoa was heavily labelled with gold, both in caput and cauda spermatozoa. The postacrosomal region was only sparsely marked in caput sperm whereas in sperm cells originating from the cauda a calix like membrane area displayed intense labelling. Some differences in the number of binding sites were also seen on sperm tails: those of caput spermatozoa show generally more Con A binding sites that those from cauda epididymal spermatozoa. No changes in the number of WGA-binding sites on sperm tails was observed during epididymal passage. The technical aspects of the indirect lectin-horse-radish-peroxidase gold technique are briefly discussed.

Electron microscopic localization of a fucose-binding protein in acrosome reacted boar spermatozoa by the fucosyl-peroxidase-gold method

In this study we have examined the behaviour and the localization of the fucose-binding protein (FBP) in boar spermatozoa during ionophore induced acrosome reaction (AR) by means of normal TEM and specimen preparation in toto. During early stages of AR the FBP is first localized at the border between equatorial segment and anterior acrosome. With the propagation of the AR the FBP is dramatically expressed and visible over the entire surface of the acrosome and equatorial segment. TEM pictures of this stages show that the FBP is associated with the OAM. At later stages of AR, when acrosomal ghost formation occur, the FBP is associated with the acrosomal ghost, and equatorial segment and to a very low degree also with the IAM. It is concluded from this data that the FBP is responsible for the specific binding of the ghost-sperm unit to the zona pellucida.

Immunohistochemical demonstration of lumbar intervertebral disc innervation in the dog

Low back pain is a common ailment in dogs, particularly in specific breeds such as the German shepherd dog. A number of structures such as facet joint capsules, ligaments, dorsal root ganglia, periosteum, vertebral endplates and meninges have been associated with this condition. Yet, in spite of all diagnostic efforts, the origin of pain remains obscure in a substantial proportion of all cases. A further structure often being involved in vertebral column disorders is the intervertebral disc. The presence of nerves, however, is a precondition for pain sensation and, consequently, structures lacking innervation can be left out of consideration as a cause for low back pain. Nerve fibres have been demonstrated at the periphery of the intervertebral disc in man, rabbit and rat. With regard to the dog, however, the extent of intervertebral disc innervation is still being disputed. The goal of the present study, therefore, was to substantiate and expand current knowledge of intervertebral disc innervation. Protein gene product (PGP) 9.5 was used for immunohistochemical examination of serial transversal and sagittal paraffin sections of lumbar discs from adult dogs. This general marker revealed nerve fibres to be confined to the periphery of the intervertebral discs. These results indicate that even limited pathological processes affecting the outer layers of the intervertebral disc are prone to cause low back pain.

Boar sperm membranes antigens. II. Reorganization of an integral membrane antigen during capacitation and acrosome reaction

The dynamics of the cell surface during the process of capacitation is impressively shown by means of a monoclonal antibody directed against the P86/5 antigen. This glycoprotein was located in the sperm plasma membrane using the colloidal gold method in combination with specimen preparation in toto. The antigen is absent at the rostral tip of non-capacitated spermatozoa, but forms clusters over the principal segment and the equatorial segment after induction of capacitation. This formation of microdomains with different properties may be a prerequisite for the onset of the acrosome reaction (AR). During AR the diffusion barrier for the P86/5 antigen breakes down and the antigen occupies now the rostral crescent-like area of the sperm head. These observations are discussed with respect to zona binding and induction of the AR in boar spermatozoa.

Immunocytological characterization of the outer acrosomal membrane (OAM) during acrosome reaction in boar

In order to study the acrosome reaction in boar, spermatozoa were incubated in a calcium-containing medium in the presence of the calcium ionophore A23187. The time course of the acrosome reaction was assessed by phase-contrast microscopy and correlated with the movement characteristics of the spermatozoa determined by means of multiple-exposure photography (MEP). Different stages of the acrosome reaction could be observed by indirect immunofluorescence using an antibody fraction raised in rabbits against the isolated outer acrosomal membrane (OAM). At the start of the acrosome reaction, a bright fluorescence located exclusively at the acrosomal cap of the sperm head could be observed, whereas after 60-120 min, the fluorescence vanished, indicating the complete loss of the OAM. However, to gain more insight into the stages of the plasma membrane and OAM during the acrosome reaction, immunoelectron-microscopical studies were performed using anti-OAM antibodies detected by the protein-A gold method. Ultrathin sections and total preparations in combination with transmission electron microscopy (TEM) confirmed, that boar spermatozoa start their acrosome reaction by a vesiculation of the plasma membrane, thus exposing the heavily labelled OAM, which is then lost as sheets or large vesicles. The newly exposed inner acrosomal membrane did not show any labelling with gold, thereby indicating clear differences in the antigenicity of both acrosomal membranes.

Morphological characteristics of boar efferent ductules and epididymal duct

The aim of the present study was to provide a comprehensive morphological analysis of the porcine epididymis in view of the specific functions being performed in different regions of this organ. Blood supply and microvasculature of efferent ductules and epididymal duct were investigated by means of corrosion casts which were analysed macroscopically and by scanning electron microscopy. This revealed blood supply to the testis and epididymis to be closely related. The capillary pattern was typical for the efferent ductules, the caput, corpus, and distal cauda epididymidis, respectively. Corrosion casts were also used to visualize the course of the efferent ductules themselves. Tissue samples from different regions of the efferent ductules and epididymal duct were examined by light microscopy and both scanning and transmission electron microscopy, with special attention being payed to transitional areas. Morphological criteria allowed the distinction of three segments within the efferent ductules and of the initial segment, proximal caput, distal caput, corpus, proximal cauda, and distal cauda regions of the epididymal duct. Components of the endocytic apparatus of efferent ductule principal cells were identified by ferritin uptake. Ultrastructural evidence of absorption in the epididymal duct was particularly prominent in proximal and distal caput. Extensive cisternae of rough endoplasmic reticulum and a well-developed Golgi apparatus were indicative of active protein synthesis and secretion especially in the distal caput and corpus regions. However, assignment of various organelles in principal cells of the epididymal duct to either absorptive or secretory pathways still remains tentative.

Distinction of gastric Helicobacter spp. in humans and domestic pets by scanning electron microscopy

BACKGROUND

A number of different Helicobacter spp. can colonize the stomach of humans and domestic pets. Difficulties encountered with primary isolation of these spiral microorganisms and their unusual inertia with respect to biochemical reactions still represent considerable obstacles to their characterization with classic tools. In addition, the high degree of similarity in the 16S rRNA sequence hampers differentiation of Helicobacter spp. using routine molecular biological assays.

MATERIALS AND METHODS

Samples from experimentally monoinfected mice, of naturally infected hosts, and of cultured strains were examined by scanning electron microscopy (SEM). In parallel, all samples were analyzed by molecular techniques to ascertain the Helicobacter spp. involved.

RESULTS

Using the mouse samples as a reference, microorganisms found in naturally infected hosts were identified by SEM as belonging to H. pylori, H. felis, or a group consisting of H. bizzozeronii and H. heilmannii. A further spiral microorganism with unique morphology was found in a dog that was positive for H. salomonis, but the organism could not be recovered from experimentally infected mice. In culture, most Helicobacter strains lost their ultrastructural characteristics.

CONCLUSIONS

When gastric Helicobacter spp. were collected from their natural habitat and examined by SEM, relevant differences could be detected between H. felis, H. bizzozeronii and H. heilmannii, and H. salomonis, respectively. SEM, therefore, seems to be a useful auxillary tool for the distinction of various gastric Helicobacter spp. as based on their ultrastructure.

The sperm acrosome: immunological analysis using specific polyclonal and monoclonal antibodies directed against the outer acrosomal membrane of boar spermatozoa

An antiserum to the purified porcine outer acrosomal membrane (OAM) was raised in female Balb/c mice and was characterized by means of an indirect ELISA. The hyperimmune serum reacted selectively with the acrosomal cap of the sperm head and showed an extremely good cross reactivity with bull and human spermatozoa when assayed by indirect immunofluorescence. Immunoelectron microscopy using the protein A-gold method further confirmed the specificity of the anti-OAM-antiserum for the OAM. In an effort to identify the OAM antigens recognized by the hyperimmune serum and to analyse the extent of cross reactivity on a molecular level, the SDS-extractable proteins were separated by SDS-PAGE, transblotted and immunoprinted using an 125J-conjugated anti-mouse-antibody. To facilitate functional and structural analysis of distinct OAM-proteins monoclonal antibodies were generated by hybridization of mouse myeloma cells with the splenocytes of female Balb/c mice immunized with the purified OAM. One fusion resulted in about 100 anti-OAM-antibodies secreting hybridoma cultures, of which about 30% showed cross reaction with human and bull spermatozoa. Four stable cell lines were selected for this study secreting antibodies directed against the outer acrosomal membrane of boar spermatozoa. Whereas the polyclonal immune mouse serum stained the entire acrosomal cap, the four hybridoma antibodies generated a patch-work-like immunofluorescence pattern over the acrosome. HPLC-ELISA of the solubilized OAM revealed first information on the nature of the corresponding membrane antigen.

Con A- and WGA-binding sites on bovine epididymal spermatozoa: TEM of specimens in toto

Binding sites for Con A and WGA were detected on bovine spermatozoa during epididymal maturation. We used colloidal gold as an EM-marker. The spermatozoa were treated according to a two-step method for lectin and colloidal gold, then adsorbed to lysine-coated nickel grids and subsequently examined by TEM in toto. Using this method we rapidly got information about the topographic distribution of lectin-binding sites. Major differences exist for WGA between caput and cauda spermatozoa. Conceding that cell-thickness poses some limitation, we consider this method to be practical and especially useful in studies concerning topographic distribution of cell surface components in single cell systems.

The glandular chambers of the placenta of the bitch in the second third of pregnancy (day 30-44): an ultrastructural, ultrahistochemical and lectinhistochemical investigation

The present study represents the first comprehensive investigation of the glandular chambers of the placenta of the bitch. We examined the glandular chambers by SEM, TEM, ultrahistochemical and lectinhistochemical methods. The glandular epithelium is a high columnar epithelium with club-shaped apical protrusions bearing short microvilli. The epithelium forms extensive folds which fill up most of the lumen of the glandular chambers. Proceeding to the placental labyrinth, the glandular chambers are covered by the tips of the chorionic tufts. The trophoblast and the glandular epithelium are separated by a thick layer of secretions. The ultrastructure cytology of the columnar epithelium is characterized by several Golgi complexes and abundant apical-located mucus vesicles with a positive dialysed iron reaction. Lectin histochemistry reveals in general a strong reaction of these mucus vesicles with all lectins used. The mucus in the lumen of the glandular chamber reacts strongly with WGA, NeuWGA, LPA and ConA. The trophoblastic villi projecting into the lumen of the glandular chambers are covered by a pseudostratified epithelium consisting of a flat basal layer and a superficial columnar one. Its cytoplasm is filled with large fusing vacuoles containing longish screw-shaped structures. No morphological equivalent of absorption is found. According to the ultrastructure of the trophoblast, the significance of the mucus in the glandular chambers in stopping the invasive growth of the trophoblast is discussed.

Fracture labelling of boar spermatozoa for the fucose-binding-protein (FBP)

Labelling of fractured boar spermatozoa with the FUC-HRP gold method for a fucose-binding-protein (FBP) gave evidence the FBP is localized in the acrosomal matrix. All fracture faces through the acrosome from the rostral end towards the equatorial segment show similar labelling pattern. This labelling is completely blocked by preincubation of the fractured tissue with focoidan.

Improved preservation of rat epididymal sperm for high-resolution low-voltage scanning electron microscopy (HR-LVSEM)

Various fixation protocols were used in an attempt to improve preservation of rat epididymal sperm for high-resolution low-voltage scanning electron microscopy (HR-LVSEM). Wash solutions and fixatives of different composition and osmolarity were tested. Paraformaldehyde and glutaraldehyde concentrations were varied between 0.5% and 3%. Ruthenium red was tested as an additive in both primary fixation and postfixation, or in postfixation alone. HR-LVSEM revealed various degrees of ruffing, folding, blebbing, and peeling off of the plasma membrane, as well as holes of different sizes. The plasma membrane overlying the acrosome and the connecting piece proved to be particularly sensitive to varying fixation conditions. Consistent topographical differences were revealed among the different domains over the sperm head. Most of the differences were considered to be artifacts. Their consistency, however, suggests that structural and biochemical differences exist either within the membrane or in the structures subjacent to the membrane. Primary fixation turned out to be less critical than postfixation. Preservation of a smooth plasma membrane without holes could only be achieved when primary fixation in low aldehyde concentrations, with or without ruthenium red, was followed by postfixation with OSO4 and 1,000 ppm ruthenium red. Examination of thin sections of the same material confirmed that even a considerable number of small holes are difficult to detect in transmission electron microscopy. These results show that with the recent increase in resolution of LVSEM there is need for further effort to improve sample processing.

Macrophage-lymphocyte cluster formation in the medullary sinus of lymph node after immunization with sheep red blood cells (SRBC)

Normally the lymphatic sinuses of the lymph node are loosely packed with lymphocytes and free macrophages as well as with macrophages adhering to the fibrocellular trabeculae. After immunization with SRBC cluster formation occurs in the medullary sinuses of rats between a central macrophage and peripherally located lymphocytes. These rosette-like clusters are nearly identical with the clusters found during primary and secondary immune response against SRBC in vitro and seem to be the in vivo equivalent for the same immune response.

Ultrastructural evidence of transplacental transport of immunoglobulin G in bitches

In dogs, passive immunity is conferred to fetuses and neonates by the transfer of maternal immunoglobulin G through the placenta during the last trimester of pregnancy and via the mammary gland after parturition, respectively. However, morphological evidence of transplacental transport is still lacking. The aim of the present study was to localize maternal immunoglobulin G in the labyrinthine zone and in the haemophagous zone of the canine placenta by means of immunohistochemistry and immunocytochemistry. In the labyrinthine zone, immunoglobulin G was detected in all the layers of the materno-fetal barrier including the fetal capillaries. Immunoreactivity was particularly prominent in maternal basement membrane material as well as in the syncytiotrophoblast. However, this evidence of transplacental transport of immunoglobulin G originated from a limited number of unevenly distributed maternal vessels only. In the cytotrophoblast of the haemophagous zone, immunoglobulin G was localized to phagolysosomes at various stages but was never detected within fetal vessels. The results indicate that maternal immunoglobulin G is degraded in cytotrophoblast cells of the hemophagous zone and, therefore, that transplacental transport is restricted to a subpopulation of maternal vessels in the labyrinthine zone.

Boar sperm membranes antigens. I. Topography of a mobile glycoprotein of the sperm cell membrane

A monoclonal antibody, designated mAb P86/5, was generated by immunization of female Balb/c mice with a membrane vesicle fraction composed of the outer acrosomal membrane and plasma membrane (PM-OAM). As determined by fluorescence microscopy and electron microscopy P86/5 recognizes a sperm plasma membrane antigen that is restricted to the sperm head. In intact spermatozoa the P86/5-antigen is distributed over the surface of the sperm head with the exception of the rostral region. By comparing the antibody binding pattern generated at 4 degrees C and 25 degrees C, it could be shown that the P86/5-antigen is capable to diffuse freely within the cell membrane overlying the acrosome whereas its lateral mobility is restricted to the post-acrosomal region. The P86/5-antigen had a molecular weight of about 78 kDa as revealed by SDS-PAGE and western blotting. The glycoprotein nature of the P86/5-antigen was established by lectin affinity chromatography.

Efferent ductules of the boar--a morphological study

The efferent ductules of the boar were investigated by means of corrosion casts, light microscopy, scanning and transmission electron microscopy. They arise from an extratesticular rete and constitute the major, caudolateral part of the ascending limb of the caput epididymidis. Ductules may be subdivided into three segments: a slightly undulating testicular segment, a highly coiled intermediate segment and a moderately coiled epididymal segment. A decrease in diameter is particularly marked from the intermediate to the epididymal segment. The epithelial transitions from the extratesticular rete to the efferent ductules and from these to the epididymal duct are clearly demarcated. The epithelium of the efferent ducts consists of principal and ciliated cells. Mononuclear leukocytes are found in the basal half. Ultrastructural evidence supports a strong absorptive activity of principal cells. Apical protrusions are not considered to be a proof of apocrine secretion but rather seem to be artifacts. The nature of membrane-bound granules of variable density remains speculative.

Cell biology of acrosomal proteins

Acrosin is a multifunctional enzyme combining several functional properties within a single molecule: the catalytic triad of the proteinase, hydrophobic domains responsible for the special membrane-associating character of the enzyme and the carbohydrate binding sites by which the molecule can bind to the zona pellucida. Acrosin occurs in the sperm acrosome as an inactive precursor, proacrosin, with a molecular mass of 53-55 kDa. Proacrosin is activated by a single proteolytic clip between Arg23 and Val24 generating the high molecular mass acrosin. The activation of proacrosin to the biologically active enzyme which occurs concomitantly with the acrosome reaction appears to be regulated on and by the zona pellucida. It is hypothesized that alternating cycles of binding to the zona, digestion of the zona and release from the zona together with the forward motility of the spermatozoon would be required to achieve penetration.

Microvasculature of the epididymis in the boar

Microvasculature of the epididymis was investigated by scanning electron microscopy of vascular corrosion casts. The basic structure of blood supply to the boar epididymis consists of two superimposed vascular networks. Capillaries surrounding the epididymal duct constitute the inner level. They form polygonal meshes around the efferent ductules whereas circular capillaries strongly predominate in the subsequent region of the caput epididymidis. This annulate feature is progressively lost from corpus to cauda, where the capillary network once again has a polygonal appearance. The outer network is composed of feeding and draining vessels. Intertubular arteries pass between the loops of the epididymal duct and give rise to longitudinally oriented vessels attributable to only one adjacent duct segment. They feed the capillary network via circular ramifications debouching in different sectors of its circumference. The sparse veins draining the capillaries encircling the efferent ductules give way to a gradually increasing number of confluent veins up to the cauda.