W. F. LOOMIS 



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All vessels were kept at 25 and all newly-detached buds were 

 removed daily with a medicine dropper so as to maintain a con- 

 stant population density within the culture. Population density, 

 temperature, nutrition, stagnation, depth of water, surface/volume 

 ratio, calcium, sodium and versene concentrations, sex and species 

 were thus held constant. 



This experiment demonstrates that under these exact conditions 

 pCOo is a controlling factor in the sexual differentiation of these 

 animals. The unusually high degree of repeatability of this experi- 

 ment makes it significant, therefore, that a totally different result 

 occurred when this experiment was repeated on a shaking machine 

 that shook similar but closed vessels for a few seconds every 

 twenty minutes day and night (Fig. 3). Under these shaken con- 

 ditions, the same experiment failed to yield any sexually differ- 

 entiated Hydra. In retrospect, this inhibitory effect of shaking is 

 due to the breaking up of the halo zone by mixing the micro- 

 environment with the macroenvironment every twenty minutes 

 around the clock. 



Fig. 3. Automatic shaker that is turned on for 5 seconds every twenty 

 minutes to destroy the halo zone by mixing the microenvironment of the 

 Hydra with the background macroenvironment. 



