Abstract
The growth pattern in Hydra littoralis was studied histologically, by methods of mitotic counting and radioautographic analysis of tritiated thymidine incorporation into cell nuclei. Some of the hydra were maintained individually for a month before experimentation and appeared to be in a mature, steady state growth condition. Mitotic figures and nuclear thymidine incorporation were abundant among each of the five classes of cells distinguished: epitheliomuscular, interstitial, nonepithelial epidermal, basal, and digestive cells. The abundance of mitotic figures was dependent on the culturing conditions, the availability of food, and the time of day. However, the axial distribution of mitotic figures was quite independent of these factors. Mitotic cells were found broadly distributed over the body column and were absent only in the distal parts of the tentacles and in the distal hypostomal gastrodermis. There was no localized region which can be called a specialized zone of growth. This pattern of mitotic activity is consistent with the tissue movements observed in normal hydra and with the general morphogenetic plasticity which hydra exhibit.
Published Version
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