The Mechanism of Urine Formation in Invertebrates

Abstract

1. In Anodonta cygnea: (a) The blood has a vapour pressure equivalent to that of a solution of ca. 0.10 per cent sodium chloride. (b) The pericardial fluid is isotonic with the blood. (c) The urine has a vapour pressure equivalent to that of a solution of ca. 0.06 per cent sodium chloride. (d) The hydrostatic pressure of the blood is ca. 6 cm. of water. (e) The calculated colloid osmotic pressure is ca. 3.8 mm. of water. (f) The average rate of filtration of fluid into the pericardium is ca. 250 c.c. in 24 hours. (g) The salt uptake from ingested phytoplankton is estimated as equivalent to 0.012. g. sodium chloride in 24 hours. (h) The loss of osmotically active substance in the urine is estimated as equivalent to 0.15 g. sodium chloride in 24 hours. 2. In Limnaea peregra the vapour pressure of the blood is equivalent to that of a solution of ca. 0.43 per cent sodium chloride. The pericardial fluid is isotonic with the blood, and the urine has a concentration equivalent to ca. 0.30 per cent sodium chloride. 3. In Limnaea stagnalis the hydrostatic pressure of the blood is ca. 8 cm. of water. The colloid osmotic pressure of the blood is ca. 2.5 cm. of water (calculated); that of the pericardial fluid is ca. 0.7 cm. of water.