FINE STRUCTURE OF THE NERVOUS SYSTEM OF HYDRA

Fine structural details of the cells and processes of the hydranenous system are reported in this paper. Ganglion cells aresmall bipolar or multipolar cells situated above the muscularprocesses of epitheliomusiular cells. An elaborate Colgi apparatusconsisting of parallel lamellae and small and large vesiclesis present in these cells. Some cells are poor in ribosomeswhile others contain numerous free ribosomes. In the ribosome-richcells, small membranous microtubules originating from the nuclearenvelope extend into the cytoplasm and neurites. The neuritesalso contain vesicles and mitochondria and terminate at thebases of cnidoblasts and on the muscular processes of epitheliomuscularcells. Specialized synapses were not observed. A second cell type contains many membrane-bounded dense granules,1000 A in diameter, and these are considered to be neurosecretorycells. Neurosecretory granules on cnidoblasts and epitheliomuscularcells. Sensory cells are small elongated cells originate inthe Golgi apparatus and are abundant in neurites which alsoterminate situated between the apical surfaces of epithelialand digestive cells. These cells are characterized by an apicalspecialization which appears to be a modified cilium. Neurosensorycells were also observed. The intimate connection of the nervoussystem with cnidoblasts suggests a role in nematocyst discharge.The finding of neurosecretory material supports the hypothesisthat the neural control of regeneration in hydra is regulatedby material released at nerve endings.