The kidney of Spinachia spinachia (L.) Flem. (Gasterosteidae, pisces) 1. Investigations of juvenile sticklebacks: anatomy, circulation and fine structure.

The opisthonephric kidney of juvenile fifteen spined stickleback (Spinachia spinachia (L.)) has been studied by light and electron microscopical investigation. The renal portal system and microcirculation has been demonstrated by casts of coloured plastic Microfil. Glomeruli are well vascularized as revealed by perfusion fixation. They contribute to the formation of urine in collaboration with a proximal tubule segment I that shows resorptive capacity. Epithelial cells of the proximal tubule segment II, which make up the bulk of the nephronic tubular mass are supposed to constitute very active secretory elements. The possible role of mucus secretion in the collecting duct-urinary duct system is discussed. Juxtaglomerulcar cells have been seen in various stages of secretion.