Prostate glands from mature and juvenileCryprozona belangeri were culturedin vitro for 8 days in single or double association with cerebral ganglia. visceral ganglionic complex and gonads obtained from adult snails. The histology of the glands was studied and compared with those of normal glands and with glands culturedin vitro without any organ association. Functional differentiation was not evident in glands cultured in isolation or in single association with gonad or brain. In double associations, involving cerebral ganglia, visceral ganglionic complex and gonad response from the gland was obtained only when the gonad was involved. The cerebral ganglia and visceral ganglionic complex acting through the gonad elicit differential responses from the prostate gland. It was concluded from thein vitro studies that the prostate gland may be dependent on a gonadal hormone for functional differentiation, which in turn is under the control of trophic factors released from the brain.