One of the puzzling features of polychaetes and some other animals is the tendency for epidermal mucus cells to become incorporated into the central nervous system (Clark, 1966). In a number of species of Nephtys an extensive prostomial mucus gland system has come into close association with the supraoesophageal ganglion of which it sometimes forms two enormous posterior lobes (Clark, 1955, 1958). Cells which are comparable to, if not homologous with, those in Nephtys are even more completely incorporated into the supraoesophageal ganglion of nereids (Bobin & Durchon, 1953; Durchon & Frezal, 1955; Hauenschild & Fischer, 1962; Herlant-Meewis & Van Damme, 1962) and glycerids (Simpson, 1959), though, unlike the situation in nephtyids, the connexion between these cells and the exterior is tenuous or even problematical in nereids and glycerids. In Pisione, superficial gland cells near the median ocelli of the trochophore larva are incorporated into the supraoesophageal ganglion at metamorphosis and form two well-defined glandular masses near the posterior eyes in the adult, losing their ducts to the exterior in the process, but retaining the appearance of gland cells (Åkesson, 1961).
PGE2 enhances Ca2+‐dependent ionic currents in the airway mucus gland cells
