Comparison of the regeneration of the hypostome with the budding process inHydra littoralis.

One group of animals has been cut close behind the tentacles and another group in the central part of the gastral region.Hydras have been fixed in Bouin in various time intervals after amputation (from 30 min to 46 h).When the hypostome is entirely closed and when both layers are conspicuous, then the hypostome looks very much like a top of the bud in development. These similarites refer to the position of the cells and their qualitative and quantitative composition.The results lead to a conclusion that zymogen cells can easily move and that in different forms of differentiation can be found in a few hours either at the place of the formation of buds or at the place of the regeneration of the hypostome.Their dedifferentiation into interstitial gastrodermal cells permitted the migration of these cells into the layer of the ectoderm and in this way the growth of the bud and the regeneration of the hypostome are made possible.The vacuolization of these cells and their change into mucous cells created the condition for the formation of new parts of the gastrodermal hypostome and for the formation of tentacles.