Ameboid cells in spermatogenic cysts of caecilian testis

Sertoli cells constitute a permanent feature of the testis lobules in caecilians irrespective of the functional state of the testis. The developing germ cells are intimately associated with the Sertoli cells, which are adherent to the basal lamina, until spermiation. There are irregularly shaped cells in the cores of the testis lobules that interact with germ cells at the face opposite to their attachment with Sertoli cells. These irregularly shaped (ameboid) cells first appear in the lumen of the cysts containing primary spermatocytes and are continually present until spermiation. We did not observe any cytoplasmic continuity between a Sertoli cell and an ameboid cell. Both light microscopic and TEM observations reveal a phagocytic role for the ameboid cells: they scavenge the residual bodies shed by spermatozoa. Organization of the ameboid cells is grossly different from that of the spermatogenic and Sertoli cells. They appear to develop from the epithelium at the juncture of the collecting ductule with the testis lobule.     

Transmission electron microscopy of impaired spermatogenesis in an avian hybrid

The mechanisms involved in the impaired spermatogenesis of male goldfinch x canary hybrids were investigated by transmission electron microscopy and compared with spermatogenesis in the testes of the parent species. In the parent species the testes were of normal structure, with the only unusual observation being that the Sertoli cells were variable in cytoplasmic electron density. In hybrid birds the Sertoli cells were either electron dense or electron lucent with respect to both nucleus and cytoplasm. In the hybrids examined in this study, no spermatozoa were produced. Spermatogenic stages were arrested without formation of synaptonemal complexes. Centrioles were abnormally arranged in both somatic and germ cells. When they moved away from the basement lamina the germ cells degenerated and were phagocytosed. No focal tight junctions were present between Sertoli cells overlying what would normally have been the basal compartment of the tubule. The basement lamina was unusually thickened, peritubular cells were abnormal in structure, and numerous plasma cells were present in the interstitial tissue. The observations reported here suggest that there was an immunological basis for degeneration of germ cells in the hybrid testis.     

Annual changes in germinal epithelium determine male reproductive classes of the cobia

Five reproductive classes of cobia Rachycentron canadum , caught along the Gulf of Mexico and the south-east Atlantic coast of the U.S.A., are described during the annual reproductive cycle. These are based upon changes in the testicular germinal epithelium and the stages of germ cells that are present: early maturation, mid maturation, late maturation, regression and regressed. During early maturation, the germinal epithelium is continuous from the testicular ducts to the periphery of the testis and active spermatogenesis occurs throughout the testis. In mid maturation, the germinal epithelium near the ducts becomes discontinuous, but it remains continuous distally. In late maturation, a discontinuous germinal epithelium extends all along the lobules to the testicular periphery; lobules are swollen with sperm and there is minimal spermatogenesis. The regression class is characterized by a discontinuous epithelium throughout the testis, sperm storage and widely scattered spermatocysts. Spermatogonial proliferation also occurs along the lobule walls and at the periphery of the testis. In regressed testes, spermatogonia exist only in a continuous or discontinuous germinal epithelium, although residual sperm are nearly always present in the lobules and ducts. The presence or absence of sperm is not an accurate indicator of reproductive classes. At the periphery of the testis in the regression and regressed classes, the distal portions of lobules elongate as cords of cells containing spermatogonia and Sertoli cells. All reproductive classes can be identified in paraffin sections, although plastic sections provide better resolution. Using maturation classes defined by changes in the germinal epithelium to describe testicular development and spermatogenesis gives a more accurate picture than does using the traditional terminology.     

Organization of interstitial tissue in the testis of the salamander Necturus maculosus (Caudata: Proteidae)

In Necturus maculosus the organization of the interstitial tissue varies according to the stage of spermatogenesis. Leydig cells at various stages of differentiation and myoid cells are always present in this tissue. The Leydig cells are undifferentiated at all phases of germ cell activity and only hypertrophy following spermiation and degeneration of Sertoli cells. These Leydig cells are structurally analogous to mammalian Leydig cells. They do not form part of the lamina propria of the seminiferous lobules and hence cannot be referred to as lobule-boundary cells previously described in the urodele testis (Lofts, '74). When the Leydig cells hypertrophy, numerous unmyelinated axons appear in the interstitial tissue. These axons, often devoid of Schwann-cell cytoplasm, occur in close proximity to Leydig cells. Because the levels of both Substance P and neurotensin increased in the testis of Necturus maculosus as Leydig cells differentiated, we concluded that these neural elements may regulate Leydig-cell function locally, through the release of neuropeptides.     

Expression of claudin-1 and -11 in immature and mature pheasant (Phasianus colchicus) testes

The expression of claudin-1 and -11, tight junctions (TJs) proteins was examined in immature and adult pheasant (Phasianus colchicus) testes. Claudin-1 and -11 cDNA were highly similar to those of human, mice, and chicken. Claudin-1 mRNA and protein (21 kDa) levels in immature testes were higher than those of adult testis. In immature testes until 6 weeks of age, Claudin-1 was found at contacts between adjacent Sertoli cells and between Sertoli cells and germ cells. In adult testis, Claudin-1 was found in early spermatocytes migrating the blood testis barrier (BTB). Blood vessels were positive for claudin-1. Claudin-11 mRNA and protein (21 kDa) increased during adulthood development of testis. In immature testis, Claudin-11 was found in apicolateral contacts between adjacent Sertoli cells, indicating its involvement in cell adhesion in immature testis. In adult testis, strong wavy Claudin-11 immunoreactivity was parallel to basal lamina at the basal part of seminiferous epithelium, indicating that Claudin-11 at the inter-Sertoli TJs may act as a structural element of the BTB. Weak Claudin-1 and -11 immunoreactivity at contacts between Sertoli cells to elongating/elongated spermatids, meiotic germ cells, and basal lamina suggests that they also participate in the cell-cell and cell-extracellular matrix adhesion in pheasant testis. Testosterone increased claudin-11 mRNA in testis organ culture and Sertoli cell primary culture, suggesting positive regulation of claudin-11 gene by androgen in Sertoli cells of pheasant testis. This is the first report on the claudins expression at BTB in avian testis.     

Hereditary defects in both germ cells and the blood-testis barrier system in as-mutant rats: evidence from spermatogonial transplantation and tracer-permeability analysis

The rat mutant allele as is located on chromosome 12. Homozygous (as/as) males show arrested spermatogenesis, mainly at the pachytene spermatocyte stage. It is not clear whether this defective spermatogenesis is caused by a failure in a somatic cell component that supports spermatogenesis or in the germ cell itself. Spermatogonial transplantation was performed to identify the genetically defective site in the as/as testis. In experiment 1, germ cells collected from as/as testes were transplanted into the testes of immunodeficient mice and normal rats. In experiment 2, normal rat germ cells were transplanted into as/as testes. The results of experiment 1 showed arrest of spermatogenesis at the pachytene spermatocyte stage, accompanied by a characteristic morphological feature, i.e., the formation of inclusion-like bodies in the cytoplasm, in both rat and mouse recipients. These results revealed the intrinsic effect of the mutant gene(s) on germ cells. In experiment 2, no restoration of spermatogenesis was detected in the recipient testes despite thorough histological examination. These results suggest that defects in a somatic cell component in as/as testes prevent the donor germ cells from colonizing and regaining their spermatogenetic ability. When the seminiferous epithelium of the as/as testis was examined by electron microscopy, no morphological abnormalities, including the formation of ectoplasmic specializations between adjacent Sertoli cells, were observed in the somatic cell components. However, when cytochrome c was applied as a tracer material, it penetrated the tight junctions between the Sertoli cells, indicating dysfunction of the blood-testis barrier in the as/as testis. The lack of restoration of spermatogenesis in the as/as testis after transplantation of normal germ cells may have been caused by the unfavorable environment in the seminiferous epithelium resulting from the incomplete barrier system between adjoining Sertoli cells. The gene(s) at the as locus may have a role in both germ cell differentiation and the establishment of the blood-testis barrier.     

Morphometric study of the prepubertal rabbit testis: germ cell numbers and seminiferous tubule dimensions

Testes from rabbits aged 1-9 weeks were examined by light microscopy. Changes in seminiferous tubule dimensions, testicular volume, and volume fraction of tubules were assessed. Germ cells and Sertoli cells were counted in round tubular cross sections and total germ cell number in each testis was estimated. Mitotic, meiotic, and degenerative activities of germ cells as well as their basal or central positions within tubules were quantified. A marked, steady increase in testis volume and in tubular length and volume occurred over the prepubertal period; but diameter underwent no significant increase and in fact decreased until week 4. Overall, tubules lengthened 40-fold and testis volume increased 25-fold; the percentage volume of the testis occupied by tubules rose from one-third neonatally to three-fifths at the onset of spermatogenesis. The ratio of germ cells to total tubular (germ and Sertoli) cells was lowest at 3 weeks. However, the total number of germ cells increased little until 3 weeks, after which it rose at a sharp rate commensurate with testis volume. Percentage of germ cells in mitosis peaked sharply at 3 weeks, dropped in subsequent weeks, and then rose at 7 weeks at the initiation of spermatogenesis. Importantly, the surge in mitosis at 3 weeks was followed by a redistribution of germ cells to a predominantly basal location from 3 to 7 weeks. Meiotic activity was sparse at 7 weeks and became abundant by 9 weeks. Germ cell degeneration remained relatively constant during weeks 1 through 6, with an increase at 7 weeks.     

The microtubule plus end-binding protein EB1 is involved in Sertoli cell plasticity in testicular seminiferous tubules

Sertoli cells of testis belong to a unique type of polarized epithelial cells and are essential for spermatogenesis. They form the blood-testis barrier at the base of seminiferous tubule. Their numerous long, microtubule-rich processes extend inward and associate with developing germ cells to sustain germ cell growth and differentiation. How Sertoli cells develop and maintain their elaborate processes has been an intriguing question. Here we showed that, by microinjecting lentiviral preparations into mouse testes of 29 days postpartum, we were able to specifically label individual Sertoli cells with GFP, thus achieving a clear view of their natural configurations together with associated germ cells in situ. Moreover, compared to other microtubule plus end-tracking proteins such as CLIP-170 and p150(Glued), EB1 was highly expressed in Sertoli cells and located along microtubule bundles in Sertoli cell processes. Stable overexpression of a GFP-tagged dominant-negative EB1 mutant disrupted microtubule organizations in cultured Sertoli cells. Furthermore, its overexpression in testis Sertoli cells altered their shapes. Sertoli cells in situ became rod-like, with decreased basal and lateral cell processes. Seminiferous tubule circularity and germ cell number were also reduced. These data indicate a requirement of proper microtubule arrays for Sertoli cell plasticity and function in testis.     

Sertoli cell proliferation in the adult testis--evidence from two fish species belonging to different orders

Germ cell survival and development critically depend on the cells' contact with Sertoli cells in the vertebrate testis. Fish and amphibians are different from mammals in that they show a cystic type of spermatogenesis in which a single germ cell clone is enclosed by and accompanied through the different stages of spermatogenesis by an accompanying group of Sertoli cells. We show that in maturing and adult testes from African catfish and Nile tilapia, Sertoli cell proliferation occurs primarily during spermatogonial proliferation, allowing the cyst-forming Sertoli cells to provide the increasing space required by the growing germ cell clone. In this regard, coincident with a dramatic increase in cyst volume and number of germ cells per cyst, in Nile tilapia, the number of Sertoli cells per cyst was strikingly increased from primary spermatogonia to spermatocyte cysts. In both African catfish and Nile tilapia, Sertoli cell proliferation is strongly reduced when germ cells have proceeded into meiosis, and stops in postmeiotic cysts. We conclude that Sertoli cell proliferation is the primary factor responsible for the increase in testis size and sperm production observed in teleost fish. In mammals, Sertoli cell proliferation in the adult testis is not observed under natural conditions. However, on the level of the individual spermatogenic cyst--similar to mammals--Sertoli cell proliferation ceases when germ cells have entered meiosis and when tight junctions are established between Sertoli cells. This suggests that fish are valid vertebrate models for studying Sertoli cell physiology.     

Hormonal induction of all stages of spermatogenesis in germ-somatic cell coculture from immature Japanese eel testis

In cultivated male eel, spermatogonia are the only germ cells present in testis. Our previous studies using an organ culture system have shown that gonadotropin and 11-ketotestosterone (11-KT, a potent androgen in teleost fishes) can induce all stages of spermatogenesis in vitro. for detailed investigation of the control mechanisms of spermatogenesis, especially of the interaction between germ cells and testicular somatic cells during 11-KT-induced spermatogenesis in vitro, we have established a new culture system in which germ cells and somatic cells are cocultured after they are aggregated into pellets by centrifugation. Germ cells (spermatogonia) and somatic cells (mainly Sertoli cells) were isolated from immature eel testis. Coculture of the isolated germ cells and somatic cells without forming aggregation did not induce spermatogenesis, even in the presence of 11-KT. In contrast, when isolated germ cells and somatic cells were formed into pellets by centrifugation and were then cultured with 11-KT for 30 days, the entire process of spermatogenesis from premitotic spermatogonia to spermatozoa was induced. However, in the absence of 11-KT in the culture medium spermatogenesis was not induced, even when germ cell and somatic cells were aggregated. These results demonstrate that physical contact of germ cells to Sertoli cells is required for inducing spermatogenesis in response to 11-KT.     

Sequential depletion of rat testicular lipids with long-chain and very long-chain polyenoic fatty acids after X-ray-induced interruption of spermatogenesis

When a single dose of X-rays is applied to the adult rat testis, stem spermatogonia are damaged, and spermatogenesis is interrupted. Supported by Sertoli cells, spermatogenic cells that endure irradiation complete their differentiation and gradually leave the testis as spermatozoa. In this study, the in vivo changes taking place a number of weeks after irradiation revealed cell-specific features of testicular lipid classes. A linear drop, taking about six weeks, in testis weight, nonlipid materials, free cholesterol, and 22:5n-6-rich glycerophospholipids took place with germ cell depletion. Sphingomyelins and ceramides with nonhydroxy very long-chain polyenoic fatty acids (n-VLCPUFA) disappeared in four weeks, together with the last spermatocytes, whereas species with 2-hydroxy VLCPUFA lasted for six weeks, disappearing with the last spermatids and spermatozoa. The amount per testis of 22:5n-6-rich triacylglycerols, unchanged for four weeks, fell between weeks 4 and 6, associating these lipids with spermatids and their residual bodies, detected as small, bright lipid droplets. In contrast, 22:5n-6-rich species of cholesterol esters and large lipid droplets increased in seminiferous tubules up to week 6, revealing they are Sertoli cell products. At week 30, the lipid and fatty acid profiles reflected the resulting permanent testicular involution. Our data highlight the importance of Sertoli cells in maintaining lipid homeostasis during normal spermatogenesis.     

Cytokines and junction restructuring events during spermatogenesis in the testis: An emerging concept of regulation

During spermatogenesis in mammalian testes, junction restructuring takes place at the Sertoli–Sertoli and Sertoli–germ cell interface, which is coupled with germ cell development, such as cell cycle progression, and translocation of the germ cell within the seminiferous epithelium. In the rat testis, restructuring of the blood–testis barrier (BTB) formed between Sertoli cells near the basement membrane and disruption of the apical ectoplasmic specialization (apical ES) between Sertoli cells and fully developed spermatids (spermatozoa) at the luminal edge of the seminiferous epithelium occur concurrently at stage VIII of the seminiferous epithelial cycle of spermatogenesis. These two processes are essential for the translocation of primary spermatocytes from the basal to the apical compartment to prepare for meiosis, and the release of spermatozoa into the lumen of the seminiferous epithelium at spermiation, respectively. Cytokines, such as TNFα and TGFβ3, are present at high levels in the microenvironment of the epithelium at this stage of the epithelial cycle. Since these cytokines were shown to disrupt the BTB integrity and germ cell adhesion, it was proposed that some cytokines released from germ cells, particularly primary spermatocytes, and Sertoli cells, would induce restructuring of the BTB and apical ES at stage VIII of the seminiferous epithelial cycle. In this review, the intricate role of cytokines and testosterone to regulate the transit of primary spermatocytes at the BTB and spermiation will be discussed. Possible regulators that mediate cytokine-induced junction restructuring, including gap junction and extracellular matrix, and the role of testosterone on junction dynamics in the testis will also be discussed.     

Histology of salmonid testes during maturation

The commonly applied classification systems of fish gonad maturity divide the maturation process into certain stages. However, the scales do not entirely reflect the continuity of the maturation process. Based on light microscope observations, the paper describes a comprehensive pattern of testicular transformations during maturation. The study was carried out on precocious underyearling and 1-year-old males of sea trout (Salmo trutta m. trutta L.), 1-year-old males of salmon (Salmo salar L.), and males of brown trout (Salmo trutta m. fario L.) aged from 7 months to 4 years. A total of 821 gonads collected during all seasons of the year were examined. The fish were fixed in Bouin's fluid. Histological slides of the mid-part of the gonad were made using the standard paraffin technique. The 3-6 microm sections were stained with Heidenhain haematoxylin. Histological changes of testes during maturation were similar in the three species studied. Immature and resting gonads contained type A spermatogonia in lobules only. The appearance of cystic structures containing type B spermatogonia in the lobules signalled the beginning of the sexual cycle in male gonads. Type B spermatogonia underwent synchronous mitotic divisions resulting in an increase in the total number of spermatogonia. As the spermatogenesis continued, the gonads showed a gradual increase in the number of cysts containing cells at all the spermatogenetic stages: type B spermatogonia, primary and secondary spermatocytes, spermatids, and spermatozoa. The well-formed spermatozoa were released to the lobule lumen once the Sertoli cells and spermatozoa connections broke up and the cyst disappeared. This was a continuous process observed throughout the spawning season. The spermatozoa were moved to the efferent duct. While some of the germ cells were completing spermatogenesis, the lobules contained less and less cysts with type B spermatogonia, primary and secondary spermatocytes, and spermatids; eventually all the cells completed spermatogenesis. At the end of maturation, vacuoles, up to 18.9 microm in final diameter (brown trout), appeared in the Sertoli cells. The vacuoles were visible in the lobule wall epithelium for a prolonged period of time. In most salmonid individuals examined, the reproductive cycles were observed to overlap. In some fish, the preparation for another cycle began very early, i.e., at the and of preceding spermatogenesis, which had not been observed before. Gonad maturation in some males was incomplete.     

Ultrastructural study of the boar seminiferous epithelium: changes in cryptorchidism

The present study compares the ultrastructural features of Sertoli cells and germ cells between scrotal testes of healthy boars and abdominal testes of unilateral and bilateral cryptorchid boars. In healthy boars, spermatogonia are flat cells lying in close association with the basal lamina. As differentiation progresses, spermatogonia acquire an oval profile and lose their contact with the basal lamina. Spermatocytes are round cells moving from the basal compartment of the seminiferous epithelium to the luminal compartment. Spermatids exhibit complex morphological changes leading to the formation of spermatozoa. Sertoli cells extend from the basal lamina to the tubular lumen. The nucleus encloses fine euchromatin and one or two nucleoli; the nuclear envelope has a few deep infoldings. The lateral cell membranes form junctional specializations that constitute the blood-testis barrier. The cytoplasm encloses smooth endoplasmic reticulum, vesicles, aggregates, and scattered mitochondria. The seminiferous epithelium of abdominal testes from unilateral and bilateral cryptorchid boars contains few spermatogonia with an abnormal appearance; the alteration in germ cell number is more severe in the bilateral disease. In unilateral cryptorchid boars, spermatogonia appear as either large pyramidal cells or roundish cells; in bilateral cryptorchid boars, spermatogonia show roundish profiles and degenerative patterns. Abdominal testes of both unilateral and bilateral cryptorchid boars are constituted by immature Sertoli cells that show abnormal cytoplasmic content, defective development of the blood-testis barrier, and atypical nuclear appearance; in bilateral cryptorchid boars, immature Sertoli cells exhibit degenerative signs. At postpubertal age, unilateral and bilateral cryptorchidism induce total arrest of spermatogenesis at spermatogonial stage as a result of an abnormal differentiation of the Sertoli cells. Moreover, the degeneration of abdominal testes initiates earlier in bilateral cryptorchidism than in unilateral cryptorchidism.     

Conserved form and function of the germinal epithelium through 500 million years of vertebrate evolution

The germinal epithelium, i.e., the site of germ cell production in males and females, has maintained a constant form and function throughout 500 million years of vertebrate evolution. The distinguishing characteristic of germinal epithelia among all vertebrates, males, and females, is the presence of germ cells among somatic epithelial cells. The somatic epithelial cells, Sertoli cells in males or follicle (granulosa) cells in females, encompass and isolate germ cells. Morphology of all vertebrate germinal epithelia conforms to the standard definition of an epithelium: epithelial cells are interconnected, border a body surface or lumen, are avascular and are supported by a basement membrane. Variation in morphology of gonads, which develop from the germinal epithelium, is correlated with the evolution of reproductive modes. In hagfishes, lampreys, and elasmobranchs, the germinal epithelia of males produce spermatocysts. A major rearrangement of testis morphology diagnoses osteichthyans: the spermatocysts are arranged in tubules or lobules. In protogynous (female to male) sex reversal in teleost fishes, female germinal epithelial cells (prefollicle cells) and oogonia transform into the first male somatic cells (Sertoli cells) and spermatogonia in the developing testis lobules. This common origin of cell types from the germinal epithelium in fishes with protogynous sex reversal supports the homology of Sertoli cells and follicle cells. Spermatogenesis in amphibians develops within spermatocysts in testis lobules. In amniotes vertebrates, the testis is composed of seminiferous tubules wherein spermatogenesis occurs radially. Emerging research indicates that some mammals do not have lifetime determinate fecundity. The fact emerged that germinal epithelia occur in the gonads of all vertebrates examined herein of both sexes and has the same form and function across all vertebrate taxa. Continued study of the form and function of the germinal epithelium in vertebrates will increasingly clarify our understanding of vertebrate reproduction. J. Morphol. 277:1014–1044, 2016. © 2016 Wiley Periodicals, Inc.     

Ultrastructural study of the Sertoli cell and the limiting membrane in the seminiferous tubule of the adult cryptorchid rat

Cryptorchidism was simulated in 13-15-day-old rats by severing the gubernaculum testis and fixing the testis to the abdominal wall. Ultrastructural examination of the testis was made 100 days after birth when a number of modifications to the seminiferous tubules were noted. Germ cells were scanty, with only occasional spermatogonia and primary spermatocytes persisting. The nuclei of Sertoli cells were regular and oval or indented in shape. Their cytoplasm was characterized by a rich smooth endoplasmic reticulum, lipid inclusions and mitochondria with tubulo-vesicular cristae indicative of stero?dogenic activity. The decrease in the number of the germ cells induced a membrane rearrangement with numerous tight junctions and interdigitations between the Sertoli cells. Sertoli cell-specific junctional complexes were very extensive. The lamina propria of the seminiferous tubule appeared thickened and folded and the multilayered basal lamina had complex folds. After fixation with glutaraldehyde containing lanthanum, the latter substance was identified in the basal intercellular spaces of the seminiferous tubules indicating that the blood-testis barrier remains functional in the intra-abdominal testis.     

Testis structure in the sys (symplastic spermatids) mouse.

Testes of mice with the recessive insertional mutation termed symplastic spermatids (sys) were assessed for structural and developmental abnormalities. Homozygous (sys/sys) males are infertile due to an abnormality in spermatogenesis leading to azoospermia. The major interruption to spermatogenesis occurs when the intercellular bridges that connect round spermatids open prematurely resulting in the formation of symplasts. Symplasts contain as many as 285 nuclei. Development of spermatids within symplasts is arrested just before, or just after, elongation of the spermatid nuclei begins. Symplasts degenerate and appear to be phagocytized by Sertoli cells and by intratubular macrophages. In addition, degeneration of young round spermatids and also spermatocytes occasionally is observed. Spermatocyte degeneration is substantial in some tubules and leaves them depleted of cells other than basal compartment cells. Sertoli cell abnormalities are prominent and include intracellular vacuolation, absence of apical processes surrounding round spermatids, degeneration, and occasional sloughing. Although reduplication and infolding of the basal lamina is also seen, this does not appear as a common phenomenon. The sys phenotype is first manifest in animals between 19 days and 22 days of age. Considerable variability is seen in testis histology of prepubertal animals; some display degenerating pachytene spermatocytes and virtually no Sertoli cell vacuoles, while others display vacuoles without apparent elevated numbers of degenerating spermatocytes. Although this study has not revealed the primary cell type(s) affected by the insertional inactivation event, it is possible that the abnormalities in the Sertoli cells are responsible for germ cell degeneration as it is generally recognized that deficits in the Sertoli cell can result in major germ cell abnormalities but not vice versa.     

Aspects of germinal cyst and sperm development in Poecilia latipinna (Teleostei: Poeciliidae).

The structure of the testis of Poecilia latipinna is described with particular reference to Sertoli cell-germ cell relationships during development and maturation of the germinal cyst. The cyst develops when primary spermatocytes become surrounded by a single layer of Sertoli cells at the testis periphery. As spermatogenesis and then spermiogenesis proceed, the cyst moves centrally in the testis toward the ducts comprising the vasa efferentia. In addition to being a structural part of the germinal cyst, the Sertoli cells phagocytize residual bodies cast off by developing spermatids and form an association with mature bodies cast off by developing spermatids and form an association with mature sperm, which resembles that observed in mammals, before the sperm are released into the vasa efferentia as a spermatozeugmata. The results of this investigation are discussed in view of what is known concerning testis structure in other teleosts and similarities between cell functions in teleosts and mammals. It is concluded that teleost Sertoli cells, teleost lobule boundary cells and mammalian Sertoli cells are homologous.