In marine Lamellibranchia--Patinopecten yessoensis (Jay) and Crenomytilus grayanus (Dunker)--neural cells, small ganglia and neural fibres have been revealed in the gonad wall. The sensitive and effector parts are presented by rather variable morphological formations. By means of histochemical and ultrastructural investigations, functional affiliation of axons is revealed and their relations to tissue elements of the gonad are demonstrated. The effector neural apparatus is formed by peptidergic, cholinergic and monoaminergic axons. Most of the axons, forming a thick network, are monoaminergic. There are some essential differences in the structure of the monoaminergic plexuses in juvenile and mature individuals. No specialized membrane differentiations, specific for sinapses, have been found.