[Development of the neural apparatus of Triaenophorus nodulosus (Cestoidea, Pseudophyllidae) during ontogenesis].

The anatomy of the nervous apparatus of Triaenophorus nodulosus at all stages of its life cycle was studied by means of Zherebtsov's hystochemical method. Judging by the cholinesterase activity the mass of nerve cells is situated in the oncospheres of the coracidium. At the procercoid stage the ortogonal nervous system arises with three pairs of the longitudinal nervous trunk. In plerocercoids the number of longitudinal trunks increases up to 7 pairs, the rough nervous plexus and inner plexus develop too, In mature, cestodes only secondary changes take place associated with the development of the genital system. Both in larvae and adults all longitudinal trunks are situated at the same level, on the border of the cortical and medullary parenchyma, and only the inner nervous plexus first described by the authors from cestodes passes through the medullary parenchyma. The arrangement of all elements of the nervous apparatus at the same level corresponds from the authors point of view to the most primitive state of the nervous system in the order Pseudophyllidea.