The responses ofScrobicularia plana(da Costa) to osmotic pressure changes

Abstract

The osmotic pressure of the blood ofScrobicularia planahas been measured when the animal is exposed to diluted sea water, and observations made on the behaviour of the animal when exposed to solutions of different osmotic pressure.The blood osmotic pressure shows no significant difference to that of the external medium except in very low salinities. The external medium with which an animal in its natural habitat comes into equilibrium is represented by the water above the mud rather than the water contained in the mud. Open animals equilibrate to 80% sea water in 4–5 h and to 60% sea water in 5–6 h. The osmotic pressure of the blood of animals that remain closed in dilute media is decreased by as little as 1·5% per hour.