The localizeation of monoamines in the central nervous system and gonad of the scallop Patin-opecten yessoensis was studied by means of the histochemical fluorescence technique. Green fluorescent cells which presumably contained catecholamines were detected in the cotices of both the anterior lobe of cerebral ganglion and the lateral lobe of visceral ganglion, whereas the cells of accessory ganglia had yelow fluorescence which suggested the presence of serotonin. The neuropil of the cerebral, pedal and visceral ganglia exhibited intense both green and yellow fluorescence. Of these three ganglia, yellow fluorescence was found most plentifully in the cerebral ganglion, and green fluorescence was predominant in the pedal and visceral ganglia. In the gonadal area, both green and yellow fluorescent fibers ran along the longitudinal axis of the gonoduct and the muscles which were found in and around the gonad. The neworks of green fluorescent varicose fibers occurred in the intestinal wall and along the epithelium around the gonad.
The present results on the localization of monoamines in the central nervous system and gonad, together with our previous experimental data, may support the idea that serotynin plays an important role in the mechanism of spawning in marine bivalves.