Micropuncture studies of the concentrations of sodium, potassium and inulin in the crayfish antennal gland.

The evidence presently available supports a ' filtration '-reabsorption hypothesis for the mechanism underlying urine formation by the antennal gland of the crayfish. This evidence has been summarized most recently by Schmidt-Nielsen & Laws (1963) and by the writer (1963). In a previous paper (Riegel, 1963) the results of measurements of chloride concentration and of osmotic pressure made on fluid removed from the antennal gland by micropuncture were presented. The present paper is concerned with an extension of micropuncture studies which ultimately are designed to yield as complete a picture as possible of the changes in water content and concentrations of electrolytes and organic molecules during the passage of urine through the antennal gland. The substances under consideration here are sodium, potassium and inulin.