ABSTRACT
Analyses have been made of the blood and urine of Palaemon serralus for the inorganic ions Na, K, Ca, Mg, Cl, SO4, the animals being kept in 50, 100 and 120 % sea water.
When the animal is in 100 % sea water the concentrations of ions in the blood, expressed as percentages of their concentrations in the medium (to the nearest 5 %) are as follows: Na, K and Cl, 85%; Ca, 105%; Mg, 20%; SO4, 10%.
When the animal is in 50% sea water the corresponding figures are: Na and Cl, 105%; K, 120%; Ca, 200%; Mg, 20%; SO4, 10%.
When the animal is in 120% sea water the corresponding figures are: Na, K and Cl, 85 % ; Ca, 115%; Mg, 30 % ; SO4, 20 %.
The concentrations of Na, K and Ca in the urine are always slightly ( 20 %) less than their concentrations in the blood. The concentration of Cl is slightly greater in the urine than in the blood (10-20 %) and the concentrations of Mg and SO4 are very much greater, by factors of up to 7 times. The relative concentrations of ions in blood and urine do not change substantially with changes in the external medium.
The antennal gland, although it plays no part in purely osmotic regulation, is no doubt partly responsible for maintaining the low blood concentrations of Mg and SO4.
I am indebted to Mr P. C. Croghan for this information (personal communication).