Ultrastructure of a spermatid transport system in the mature proglottids of experimental Taenia crassiceps (WFU strain)

In classical textbooks of parasitology, the mature proglottids of taeniids are depicted as structures in which the individual testis are connected to the vas deferens through the vas efferens system, usually depicted as a network of channels. From our morphological analyses of proglottids in the cestode Taenia crassiceps, we have been unable to identify this channel network. It is unclear how the spermatids are transported from the testes to the vas deferens, as is unresolved the location of the cells responsible for the production of testosterone (Leydig cells) or the possible equivalent of Sertoli cells, necessary for the differentiation process of these cells. In this experimental work, we have examined the ultrastructure of tissues in the vicinity of the vas deferens in mature proglottids obtained from the intestines of hamsters infected with cysticerci from the peritoneum of infected mice. Worm tissues were fixed, processed, and sectioned for transmission electron microscopy. Significant areas of the testis epithelia emitted cytoplasmic projections surrounded by extracellular matrix, where they appear as septated pockets enclosing free axonemes and spermatids. Vas efferens walls are made up of nucleated cells with cytoplasm annealing to each other through cell membrane junctions. Lodged between the junctions are membrane-bound pouches with dense granules found as aggregates or aligned in a semicircular array. The efferens wall exhibits numerous spermatids emerging into the lumen, an observation that suggests the epithelial wall may have the maturing functions of Sertoli cells of vertebrates. Large cells adjacent to the vas efferens contained prominent rough endoplasmic reticulum and large mitochondria, characteristics described for Leydig cells of vertebrates. Our observations suggest that taeniid spermatids are either transported from the testes to the vas system by epithelial pockets or that the epithelial pockets may be cross-sections of a highly coiled vas efferens system.