The testis was surrounded by the tunica albuginea, a thin capsule of connective tissue (Fig 1 and Fig 2), from which thin septum originated and extended into the parenchyma of the testis. Among these septa, the seminiferous tubules were found (
Baradi and Rao, 1980,
Heyn et al., 1997, Mehraein and Negahdar, 2011,
Villagra et al., 2018 and
Kocakoglu et al., 2023).
The outer surface of tunica albugenia was folded. These folds were longitudinal and transverse with the depressions or troughs in between them. Ridges and throughs were also noticed in these folds at higher magnification (Fig 3). These ridges and folds may be attributed to the increase in surface area
(Saleem et al., 2018). No microvilli, intercellular stomata or gaps were evident on the parietal layer (
Baradi and Rao, 1980). The filamentous processes were observed in the mesothelial cells of tunica albugenia (Fig 4), which were likely to serve as attachment devices between mesothelial cells (
Simionescu and Simionescu, 1977). These cells were subjected to mechanical stress as scrotal, inguinal and abdominal positions of the testis are achievable.
Seminiferous tubules appeared in the form of cylinders which were longitudinally arranged (Fig 5 and Fig 6). Two types of free space continuous with each other were produced: open, triangular interstices between three adjacent cylinders (Fig 6) and flat, biconcave interstices between two adjacent cylinders (
Clark, 1975 and
Saleem et al., 2018). The seminiferous epithelium consisted of spermatogonial cells at different stages of development separated from each other by interstitial connective tissue
(Pires et al., 2012 and
Saleem et al., 2018). The seminiferous epithelium comprised of mainly spermatogonia and primary spermatocytes in neonatal goats (Fig 7), where as the spermatids were visible in pre-pubertal and pubertal non-descript goats (Fig 8).
The spermatogonia cells, those initiate the development of the germ line, were isolated oval cells arranged on the tubule basal membrane, in contact with a Sertoli cell
(Villagra et al., 2018). The primary spermatocytes were rounded cells placed adjacent to the spermatogonial cells (Fig 6 and Fig 8). The secondary spermatocytes were also rounded cells, but were comparatively smaller in size than that of the primary spermatocytes (Fig 8). The early spermatids were oval shaped cells, which were located towards the lumen of the seminiferous tubules along with the elongated late spermatid cells (Fig 8). The present findings were in line with the findings of
Villagra et al., (2018) in frogs. These cells undergo a process called spermiogenesis, the last stage of spermatogenesis, which involves a complete reorganization of the nucleus
(Villagra et al., 2018).
Our observations show that, until the spermatogenesis process is completed, all the cells of the germ cell line are in close relationship with at least one Sertoli cell
(Choudhary et al., 2015 and
Villagra et al., 2018). The sertoli cells were tall columnar cells with few cell populations in the germinal epithelium (Fig 8). They were extended from the basal membrane of the seminiferous epithelium up to the lumen of the tubule. The Sertoli cells, which nurture maturing germ cells, play an important role in the process of spermatogenesis. Although a number of studies in many mammals have been made on their morphological characteristics using light and transmission electron microscopy (
Elftman 1963;
Ploen and Ritzen, 1984;
Ekstedt et al., 1986), scanning electron microscopic configuration was never accurately described, probably because of its complicated morphological features as well as its close attachment to germ cells. In addition, the three-dimensional structure of the Sertoli cell in the rat and monkey was also reconstructed from electron micrographs of semiserial sections (
Wong and Russell, 1983;
Weber et al., 1983; Russell et al., 1986). Moreover,
Hamasaki and Murakami (1981) described in detail certain processes of the rat Sertoli cell by scanning electron microscopy. The results of this work demonstrated that there is a close relationship between germ cells and Sertoli cells during spermatogenesis, a fact with important functional significance. It is generally accepted that the shape of the Sertoli cell continually changes in association with the progress of spermatids formation ((
Elftman 1963). Russell and co-workers (
Wong and Russell, 1983;
Russell et al., 1986) classified the configuration of the Sertoli cell into Type A and Type B. The cell observed in this study corresponds to their Type A. In the basal portion of the seminiferous epithelium, the germ cells seem to be situated in compartments enclosed by adjacent Sertoli cells. Furthermore, they were located in successive recesses as viewed from the basal aspect. These recesses were formed by continuous Sertoli cells, presumably being equivalent to the so-called basal compartment. The tight junctions and desmosomes among somatic cells indicate the existence of a hemato-testicular barrier in charge of maintaining the differences in the composition of the germinal and interstitial compartments. This barrier would give rise to an adequate medium for the development of the germ line cells, as suggested by
Yoshida (2016), protecting them from pathogens and toxins that cannot pass through the intercellular junctions. Another function of Sertoli cells is to act as a structural support for germ cells (
Gavrila and Mircea, 2001;
Griswold and McLean, 2006 and
Kopera et al., 2010).
The interstitium was made up of randomly arranged collagen bundles
(Heyn et al., 1997). The arrangement of the interstitial cells of the testis in relation to the capillaries and lymphatic channels, in particular, was easier to visualize in SEM (
Connell, 1976). The intertubular vascular connective tissue contained Leydig cells, which were polyhedral or rounded in shape located mainly at wider locations where they were bounded by more than two seminiferous tubules (Fig 9). The present observation was similar to the reports given by
Ezeasor (1985) in goat and
Villagra et al., (2018) in frog. The cells were generally scanty, mostly occurring singly close to vascular elements. The cells were generally oval-elongated in shape (
Ezeasor, 1985 and
Villagra et al., 2018). The peritubular cells in the seminiferous tubules were mostly occupied by the spindle shaped myo-fibrocytes having contractile activity (Fig 10). The regular contraction of these cells, propels the mature germ cells towards the lumen of the seminiferous tubules from their periphery for spermiation.
The mediastinum rete was an elongated epithelial-connective tissue structure, which followed the major axis of the testis (
Messing 1877,
Klein and Noble-Smith 1880;
Hill, 1906;
Benoit, 1926;
Lasserre and Armingaud, 1934;
Schulte, 1937;
Short et al., 1967; Setchell, 1970 and
Dym, 1974). The mediastinal rete testis area contained many cavities of intercommunicating channels supported by connective tissue pillars (Fig 11). conical columns were observed separating the channels of rete testis (
Roosen-Runge and Holstein, 1978). The present findings were in agreement with the reports of
Burgos et al., (1979) in monkey,
Nykanen (1980) in rat and
Goyal and Williams (1987) in goat. Delicate ridges were present on the walls of the rete, possible overarching subepithelial blood vessels. These ridges were quite prominent in the pubertal period (Fig 12).
The rete and the seminiferous tubules were usually separated by only a thin layer of dense connective tissue (Fig 13). Thus, the seminiferous tubules caused modifications in the contour of the inner rete walls (
Nykanen, 1980). Blood vessels with RBC were also observed in the areas of rete testis. The rete cavities were nearly devoid of spermatozoa (
Nykanen, 1980). The rete testis, regardless of its location, was lined by flat cuboidal cells (Fig 14). The present report was in line with the observation of
Goyal and Williams (1987) in goat. The epithelial cells had “cobble-stoned’’ appearance (
Nykanen, 1980). The epithelial cells possess few microvilli and a centrally located flagellum at the luminal border (
Leeson, 1962 and
Goyal and Williams, 1987). The epithelium of the mediastinum rete was lying on a layer of connective tissue, which was usually quite thin (
Nykanen, 1980). The subepithelial loose connective tissue had a fine structure typical of this type of tissue and might have a role in the fluid physiology of the rete testis (
Nykanen, 1980).
