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The role of free amino acids as solutes for cell volume regulation in marine molluscs under salinity stress is well established. Under hypoosmotic stress the intracellular concentrations of amino acids decrease by extrusion from the cells, followed by deamination and/or excretion. However, no uncontroversial evidence is available about mechanisms involved in the enlargement of the free amino acid pool during hyperosmotic stress.Since anaerobic metabolism in bivalves can result in the accumulation of the amino acids alanine and glutamate, a possible contribution of the anaerobic metabolic pathways to the osmotic adjustment of the cell during hyperosmotic stress has been considered. The net gain of amino acids implies the fixation of ammonia to 2-0x0

Abstract--1. Glycogen content was measured in the sea mussel Mytilus edulis, and found to be present in amounts ranging from 10 to 35 per cent dry weight of the soft parts.2. The annual glycogen cycle was followed for five different fractions: the digestive gland, muscles (including those of the foot), gills, mantle and residue. Seasonal changes in giUs and muscles were much smaller than in the other tissues.3. The annual glycogen cycle for the total animal consisted of a rapid increase in spring and early summer, followed by small fluctuations in the late summer. In autumn and early winter there was a gradual decline reaching a minimum of about 10 per cent in February and March.4. There was an interrelation between seasonal changes in dry weight and the percentage of glycogen.