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Fine structural details of the cells and processes of the hydra nenous system are reported in this paper. Ganglion cells are small bipolar or multipolar cells situated above the muscular processes of epitheliomusiular cells. An elaborate Colgi apparatus consisting of parallel lamellae and small and large vesicles is present in these cells. Some cells are poor in ribosomes while others contain numerous free ribosomes. In the ribosome-rich cells, small membranous microtubules originating from the nuclear envelope extend into the cytoplasm and neurites. The neurites also contain vesicles and mitochondria and terminate at the bases of cnidoblasts and on the muscular processes of epitheliomuscular cells. 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 neurosecretory cells. Neurosecretory granules on cnidoblasts and epitheliomuscular cells. Sensory cells are small elongated cells originate in the Golgi apparatus and are abundant in neurites which also terminate situated between the apical surfaces of epithelial and digestive cells. These cells are characterized by an apical specialization which appears to be a modified cilium. Neurosensory cells were also observed. The intimate connection of the nervous system with cnidoblasts suggests a role in nematocyst discharge. The finding of neurosecretory material supports the hypothesis that the neural control of regeneration in hydra is regulated by material released at nerve endings.
LFNTZ et al. (Sun,) studied this question.