The role of the atrial diverticulum in the copulatory apparatus of the terrestrial flatworm Platydemus manokwari de Beauchamp (Tricladida : Terricola)

Diverticula are present in the copulatory organs of many species of the Ter ricola. In some species these structures are copulatory bursae or resorptiv e vesicles. The function of diverticula present in the copulatory organs in species of Dolichoplana and Platydemus (Rhynchodemidae), in Australoplana (Geoplanidae) and in some other caenoplaninid genera has been an enigma. Fr om histochemical and other investigations of the ventro-posterior copulator y diverticulum in Platydemus manokwari de Beauchamp, it is evident that thi s structure is neither a copulatory bursa, resorptive vesicle nor a uterus. It is an adhesive gland producing a viscid, collagen-like fibrous glycopro tein derived from two secretory elements present in the gland. The secretio n is expelled during cocoon laying to adhere the cocoon onto the substratum . The diverticulum appears late in the development of the copulatory organs , and is present when the gonopore is patent; this has implications for the taxonomy of platydemid flatworms.