THE EFFECT OF OSMOTIC HYSTERESIS ON VOLUME REGULATION IN MYTILUS-EDULIS

1. When Mytilus edulis was transferred from 600 to 300 mOsm, the hemolymph osmotic pressure decreased with a rate constant of 0.077 .+-. 0.0097. Irrigation of the mantle cavity increased the rate constant to 0.50 .+-. 0.05. 2. When mussels were transferred from 300 to 600 mOsm, the hemolymph osmotic pressure increased with a rate constant of 0.721 .+-. 0.095. Inhibition of lateral cilia with dopamine decreased the rate constant to 0.615 .+-. 0.0509. 3. During hypoosmotic stress, irrigation of the mantle cavity increased the magnitude of water gain, sped recovery in whole animals but slowed recovery in isolated tissue. 4. During hyperosmotic stress, addition of dopamine decreased the magnitude of water loss and sped recovery in whole animals, and isolated tissue.