ELECTROPHYSIOLOGIC INDICATIONS OF THE OSMOREGULATORY ROLE OF THE TELEOST UROPHYSIS.

Tilapia mossambica when placed in salt water shows an increase in the frequency of spontaneous discharges in some neurosecretory fibers in the urophysis of the caudal neurosecretory system. Exposure to tap water usually depresses this activity. The nature of the ion-regulatory action of the caudal neurosecretory system of teleosts remains conjectural, but the data currently available indicate the possible production of two kinds of neurohormones, one which favors ion movement in the normal direction and another which has the opposite eJffect in response to abnormal osmotic circumstances.