REGENERATION AND REPRODUCTION OF IRRADIATED GREEN HYDRA (CNIDARIA)

Green hydras (Hydra viridissima), which contain symbiotic algae of the genus Chlorella in their digestive cells, when exposed to UV light (253,5-mu-m, 1,2 J S-1 m-2) for 2, 3 and 5 minutes from a 1 m distance become damaged and shrunk, whereas those exposed for 5 minutes die. The surface mucous layer and much of the hypostome was damaged. During regeneration of surviving individuals these parts recover rapidly In this, as in many previous experiments, zymogen cells had the ability to dedifferentiate into gastrodermal interstitial cells and to differentiate into mucous cells. During the regeneration all these stages could be seen on histological preparations. Changes of zymogen cells were equal to those in the regeneration and in the formation of new buds during the vegetative reproduction. In this work it has been ascertained that UV irradiation increased the number of buds on green hydra, especially in groups irradiated for 2 and 3 minutes. In periods after exposure, it seems that the number and the volume of algae increased in the gastrodermal cells.