ABSTRACT
In all aquatic molluscs examined (Anodonta—Picken, 1937; Haliotis—Harrison, 1962; Octopus—Potts & Martin, 1963), blood is filtered through the wall of the heart (or branchial heart appendages in Octopus) into the pericardium. The pericardial fluid passes to the kidney, where secretion and reabsorption modify it to form the final urine. In the terrestrial pulmonates, however (Achatina—Martin, Harrison & Stewart, 1953; Helix pomatia and Archachatina—Vorvohl, 1961), blood appears to be filtered directly into the kidney, and reabsorption takes place in the ureter. In the present paper the inorganic composition of the urine of the freshwater prosobranch Viviparus viviparas is analysed and the rate of urine production is measured. The mechanism of urine formation is then examined in some detail.
