Sea water and hemolymph osmolalities were measured with
a Wescor Model 51OOC vapor pressure osmometer. Approximately
100 ~1 of hemolymph was sampled by syringe
through the arthrodial membrane at the base of a walking
leg and quickly expelled onto a piece of plastic film. Osmotic
pressure was measured in an 8-~1 aliquot of hemolymph
placed on a filter paper disc in the osmometer. The
total time that elapsed between expelling the sample onto
the plastic film and placing the aliquot in the osmometer
was approximately 5 s