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An in vitro investigation has clarified the neuroendocrine mechanism responsible for the differentiation of the female gonad in the protandrous hermaphrodite Crepidula fornicata. The male gonads were used as target organs; in some experiments they were brought to a uniform resting state by prior decerebration of donor animals. When isolated in culture, most of the male gonad degenerates, leaving only the stem cells lining the wall of the acini. No ovarian autodifferentiation has been observed. A masculinizing factor, released by the nervous ganglia during the male phase, controls spermatogonial mitosis and maintenance of male differentiation. A feminizing factor, secreted by the nervous ganglia during sex inversion and the female phase and present in the hemolymph, initiates oogonial mitosis and female differentiation in the male phase gonad.

The innervation of the endocrine optic gland of Sepia, which controls sexual maturation, was studied by immunocytochemistry. Anti-FMRFamide (Phe-Met-Arg-Phe-NH2) serum revealed immunoreactive neurons in the olfactory and basal-dorsal lobe of the supra-esophageal brain mass. The axons of these neurons form a network from which fibers run to the optic gland. The fibers form many varicosities on the glandular cells, indicating synaptic innervation. Apparently, the two brain lobes containing the immunopositive cells function as a unit where visual and olfactory cues are integrated to regulate the endocrine activity of the optic gland.