Structure of the corpuscles of Stannius in the euryhaline teleost Takifugu niphobles (Tetraodontiformes, Teleostei), with special regard to vascularization and extravascular channel system.

Vascularization and the extravascular channel system of the corpuscles of Stannius in a euryhaline teleost, Takifugu niphobles, were studied by scanning electron microscopy of the vascular corrosion cast, and histochemistry of exogenously injected horseradish peroxidase as a macromolecular tracer. The corpuscles were apposed to the caudal part of the ureter, away from the mesonephric kidney, and were supplied with arterioles from the genital artery running ventrally as a ramus of the dorsal aorta. Elaborate capillary networks irrigating the glandular lobules were collected by the venules to drain into the posterior cardinal veins. Electron microscopic examination of the glands demonstrated two types of secretory cells, type-1 cells with large granules, and type-2 cells with smaller granules. The type-1 cells, predominating in the gland, occasionally showed exocytosis of the secretory granules, mainly into intercellular spaces between adjoining cells. Exocytosis was also evident in the type-2 cells. The tracer molecule injected was visualized histochemically within the capillary lumina and intercellular spaces throughout the gland. The labelled spaces intercommunicated with each other to form an extensive extravascular channel system as a diffusing pathway within the gland. The possible role of this system in hormone transport and/or storage was discussed.