Abstract
1. The mechanism underlying diuresis in Rhodnius has been investigated. 2. An isolated preparation of the Malpighian tubules of a 5th-instar larva is described. 3. The rate of secretion by such a preparation, isolated in a drop of haemolymph, is at first high but soon falls to a low level. It can be restored by the addition of haemolymph taken from an insect during diuresis. 4. It has been shown that diuresis is promoted by some substance, presumably a neurohormone, which can be extracted from the posterior neurosecretory cells of the fused ganglionic mass situated in the mesothorax.