Fine structural changes in the nervous system of the regenerating hydra

The fine structure of neurons from regenerating hydra was studied. The ganglion cells of regenerating hydra in contrast to those of normal hydra contain denser and sometimes multiple nucleoli, polyribosomes, and membrane‐bounded accumulations of dense homogeneous material which appears to be elaborated by the Golgi apparatus. During regeneration, membrane‐bounded dense granules disappear from the perikaryon of neurosecretory cells and accumulate in the processes. They are released by fusion of the vesicle membrane with the plasma membrane of the neurite. A large number of intermediate stages of differentiation of neurons from interstitial cells are present after 12 hours of regeneration. These observations support the hypothesis that neurosecretory substance released at nerve terminals plays a significant role in the regulation of growth and differentiation in the regenerating hydra.