Observations on the histogenesis of nervous tissue in Diphyllobothrium dendriticum Nitzsch, 1824 (Cestoda, Pseudophyllidea).

The mode of growth of the populations of cells within and immediately surrounding the main lateral nerve cords in the actively growing, immature Diphyllobothrium dendriticum was studied by the use of 3H-thymidine autoradiography. The population of nerve cells within the nerve cord grows only on account of cell migration from the surrounding parenchyma. No mitotic figures were observed in the nerve cords. The rate of growth is high. Within a period of cultivation for 2 days in hamster 34% of the nerve cells within the nerve cords have arrived from the parenchyma. These cells can be considered as cells at the starting point for differentiation into nerve cells. The protective layer of binding cells around the nerve cords also grows on a-count of cells migrating from the parenchyma. The binding cells actively move from the outer regions of the layer inwards close to t-e nerve cord. As stem cells for these types of cell differentiation serve the highly basophilic, actively dividing germinative cells.