OBSERVATIONS ON HYDRA AND PELMATOHYDRA UNDER DETERMINED HYDROGEN ION CONCENTRATION

¹ UNIVERSITY OF VIRGINIA

1. The optimum range of hydrogen ion concentration for both Hydra viridissima and Pelmatohydra oligactis lies within the range pH 7.8 and 8.0.

2. Polyps allowed to develop pronounced dedifferentiation and resorption in a high hydrogen ion concentration (low pH) were induced to completely restore their lost parts when the medium was altered to be within the optimum range of pH.

3. Hydras carried within the optimum range of pH were subjected to periods of inanition as great as twenty five days without showing any external evidence of dedifferentiation and resorption at the end of this period.

4. Histological preparation of polyps, kept for long periods without food at the optimum hydrogen ion concentration, show slight evidence histologically of dedifferentiation and resorption at a critical period. This critical period appears somewhere between ten and seventeen days after inanition within the optimum range of pH. Such microscopic dedifferentiation and resorption are not progressive; for after this critical period has passed no further histological evidence of dedifferentiation and resorption has been observed.

(b) This microscopic dedifferentiation and resorption usually appear at the tips of the tentacles; but in one case we have seen it involve the basal third of the polyp and not the tentacles.

5. Hydras subjected to long periods of inanition within the optimum range of pH accept food readily. There is, therefore, no evidence of depression given by these polyps.

6. Dedifferentiation and resorption are induced rather by unfavorable hydrogen ion concentration than by inanition.