THE NERVOUS-SYSTEM OF TRICLADIDA .3. NEUROANATOMY OF DENDROCOELUM-LACTEUM AND POLYCELIS-TENUIS (PLATHELMINTHES, PALUDICOLA) - AN IMMUNOCYTOCHEMICAL STUDY

The organization of the nervous system of Dendrocoelum lacteum (Tricla dida, Paludicola, Dendrocelidae) and Polycelis tenuis (Tricladida, Pal udicola, Planariidae) was studied by immunocytochemical double stainin g, using neuropeptide RFamide and serotonin (5-HT) antisera on cryosec tions. The study confirmed the status of the min nerve cords (MCs) as the most important and stable of the longitudinal cords and supported the hypothesis of a common phylogenetic origin of the MCs in flatworms . The ganglion-like structures along the MCs at the beginning of trans verse commissures and lateral branches showed a close contact with ven tral fibres of the submuscular nerve plexus indicating an origin from crossing points of insunken ring commissures. The distributional patte rn and morphology of the RFamide-IR cell bodies in D. lacteum correspo nded to that of neurosecretory cells. Most RFamide-IR cells were unipo lar and rounded while 5-HT-IR cells were uni- bi- and multipolar. The neuropile consisted of a dense RFamide-IR and a loose 5-HT-IR network. RFamide dominated in all parts of the genital plexus.