The Osmotic and Ionic Regulation of Asellus Aquaticus (L.)

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Abstract
1. The freshwater isopod Asellus aquaticus can be adapted to media ranging in concentration from 0.088 mM./l. NaCl to 200 mM./l. NaCl. 2. In fresh water O.P.1 has a mean value of 150.5 mM./l. NaCl. In more concentrated media O.P.1 approaches isotonicity with the medium. 3. The mean ion concentrations of the haemolymph of animals in fresh water are Na1 = 137 m-equiv./l., Cl1 = 125 m-equiv./l. and K1 = 7.4 m-equiv./l. 4. Na and Cl account for most of O.P.1 throughout the viable range of haemolymph concentration. 5. Evidence is presented which suggests that the animal is fairly permeable to salts and water. 6. During 8 days' starvation there is no change in O.P.1, Na1 or Cl1. Sodium and chloride lost from the body can therefore be replaced by active uptake in the absence of food.