No abstract

Specific antibodies against histamine were used to demonstrate the occurrence and cellular distribution of histamine-like immunoreactivity in three species of flatworms (phylum Platyhelminthes). In the parasitic cestode Diphyllobothrium dendriticum, histamine-reactivity was found in neurons of the main nerve cords, and in cells lining the central and peripheral excretory ducts. In the free-living microturbellarian Microstomum lineare and in the planarian Polycelis nigra, histamine-immunoreactivity was restricted to cells and fibres of the nervous system. The occurrence of histamine or a related substance in the nervous system of flatworms, which represent primary bilateria, indicates the importance of this neuroactive substance in the animal kingdom.

No abstract

An electron dense marker, lanthanum nitrate, was injected into the excretory ducts of living plerocercoids of Diphyllobothrium dendriticum and the observations made by electron microscopy. The contractions of the plerocercoid spread the marker into the excretory system, and the distribution was found to be irregular both within the ducts and from one duct to another. Communication between the smallest ducts and the rest of the excretory system was noted. The marker was also introduced from the surrounding medium, in this case the fixative. It was found to flush into the excretory ducts through the pore in the tail and to be distributed into the ducts in the same way as the injected marker. No other pores were observed through the tegument other than the excretory pore in the tail by either method. In ultrastructure the duct wall is similar to that of other cestodes. The distributive role of the excretory system is discussed, including a comparison between the tegument and the duct wall.

Lindroos, P. 1984. Observations on the extracellular spaces and intercellular junctions in Diphyffobothriurn dendriticurn (Cestoda). (Institute of Biology, Abo Akademi, Finland.)-Acta 2001. (Stockh.) 65, 153-158.Extracellular spaces and intercellular junctions were studied in adult Diphylfobothriurn dendriticum after lanthanum nitrate infiltration. The parasitic tapeworms absorb nutrients across the whole body surface, the syncytial tegument. The results indicate that the distribution of nutrients can occur both in the extracellular stroma and in the intracellular compartment, through intercellular junctions of the gap junction-type. The fibrous basal lamina of the tegument forms a large extracellular compartment communicating through narrow interstices in the subtegument with extracellular lacunae in the parenchyma. Intercellular junctions of the gap junction-type frequently occur between the tegument cell bodies, as well as between tegument and parenchymal cells. According to the function of these cells in nutrient uptake and storage, metabolic coupling seemed the most likely mission for these junctions. Thus it can be concluded that the extracellular spaces and the intercellular junctions create the possibilities for an efficient distribution of nutrients in this tapeworm.