Morphology and histology of the male reproductive tract of Caecilia thompsoni (amphibia: Gymnophiona)

We studied the male reproductive tract of individuals of different body sizes of Caecilia thompsoni to describe morphological characteristics in comparison to other Gymnophiona. The reproductive tract consists of paired testes segmented into chains of primary and secondary lobes, sperm ducts that empty to Wolffian ducts, the cloaca that receives the Wolffian ducts and possesses a phallodeum. Müllerian ducts are present and develop into paired glands that empty into the cloacal urodeum. Testicular secondary lobes contain lobules with cysts of the entire germinal cell line, whereas primary lobes, in the terminal ends of the chains, only have spermagonia, Sertoli cells, and connective tissue. The smallest individual examined (21 cm body length) was immature and only possessed a few testicular primary lobes. Once the individuals reach sexual maturity, the morphological characteristics are quite consistent at macroscopic and histological level among males of very different body sizes. The histological features of the Wolffian and Müllerian glands suggest a complementary secretory role between the two ducts. In the cloaca we found the propulsor muscle, venous sinuses, and blind sacs in the phallodeum, which differentiate C. thompsoni from other species of the genus. Despite these slight differences, the general morphological characteristics, both macroscopic and microscopic, of the reproductive tracts of adult males of C. thompsoni follow the pattern known for the reproductively active males of Gymnophiona.

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.

Spermiogenesis in caeciliansIchthyophis tricolor andUraeotyphlus cf. narayani (Amphibia: Gymnophiona): Analysis by light and transmission electron microscopy

Spermiogenesis, known as spermateleosis in lower vertebrates, is the transformation of the round spermatid into a highly specialized spermatozoon with a species-specific structure. Spermateleosis and sperm morphology of two species of caecilians, Ichthyophis tricolor and Uraeotyphlus cf. narayani, from the Western Ghats of Kerala, India, were studied using light and transmission electron microscopy. Spermateleosis is described in early, mid-, and late phases. During the early phase, the spermatid nucleus does not elongate, but the acrosome vesicle is Golgi-derived and its material is produced as a homogeneous substance rather than as discrete granules. In development of the acrosome, the centrioles shift in position to the lower half of the cell. The acrosomal vesicles take the full shape of the acrosome with the establishment of the perforatorium in midphase. An endonuclear canal develops and accommodates the perforatorium. The incipient flagellum is laid down when the proximal centriole attaches to the posterior side of the nucleus and the distal centriole connects to the proximal centriole, which forms the basal granule of the acrosome. The axial fiber also appears during midphase. The mitochondria shift in position to the posterior pole of the cell to commence establishment of the midphase. Late phase is characterized by nuclear condensation and elongation. Consequently, the final organization of the sperm is established with the head containing the nucleus and the acrosome. The undulating membrane separates the axoneme and axial fiber. Most of the cytoplasm is lost as residual bodies.

Stages in spermatogenesis of two species of caecilians,Ichthyophis tricolor andUraeotyphlus cf. narayani (Amphibia: Gymnophiona): Light and electron microscopic study

The sequential changes during spermatogenesis in the testis of two species of caecilians, Ichthyophis tricolor (Ichthyophiidae) and Uraeotyphlus cf. narayani (Uraeotyphliidae), of Western Ghats of Kerala, India, were traced using both histological techniques and transmission electron microscopy. The cell nests were assigned to stages in spermatogenesis based on the classification of van Oordt (1956, Thesis, Utrecht University). To the best of our knowledge, this is the first identification and ultrastructural description of stages in spermatogenesis in caecilians. The article illustrates not only the stages, but also the cell divisions, mitotic and meiotic, as specified. The observations indicate that, although caecilians have undergone considerable modifications in morphology and anatomy, including reproductive anatomy, in the context of a subterranean and concealed life, they appear to have conserved the typical amphibian pattern of spermatogenesis for the events of development of spermatids.

Sertoli cells in the testis of caecilians,Ichthyophis tricolor andUraeotyphlus cf. narayani (Amphibia: Gymnophiona): Light and electron microscopic perspective

The caecilians have evolved a unique pattern of cystic spermatogenesis in which cysts representing different stages in spermatogenesis coexist in a testis lobule. We examined unsettled issues relating to the organization of the caecilian testis lobules, including the occurrence of a fatty matrix, the possibility of both peripheral and central Sertoli cells, the origin of Sertoli cells from follicular cells, and the disengagement of older Sertoli cells to become loose central Sertoli cells. We subjected the testis of Ichthyophis tricolor (Ichthyophiidae) and Uraeotyphlus cf. narayani (Uraeotyphliidae) from the Western Ghats of Kerala, India, to light and transmission electron microscopic studies. Irrespective of the functional state of the testis, whether active or regressed, Sertoli cells constitute a permanent feature of the lobules. The tall Sertoli cells adherent to the basal lamina with basally located pleomorphic nuclei extend deeper into the lobule to meet at the core. There they provide for association of germ cells at different stages of differentiation, an aspect that has earlier been misconceived as the fatty matrix. Germ cells up to the 4-cell stage remain in the intercalating region of the Sertoli cells and they are located at the apices of the Sertoli cells from the 8-cell stage onwards. The developing germ cells are intimately associated with the Sertoli cell adherent to the basal lamina until spermiation. There are ameboid cells in the core of the lobules that appear to interact with the germ cells at the face opposite to their attachment with the Sertoli cells. Adherence of the Sertoli cells to the basal lamina is a permanent feature of the caecilian testicular lobules. The ameboid cells in the core are neither Sertoli cells nor their degeneration products.