24 M. H. JACOBS. 



condition. Even the same eggs which had been centrifuged after 

 exposure to CO 2 and had failed to stratify showed the normal 

 behavior when the process was repeated after they had stood ex- 

 posed to the air for 30 minutes. 



It seemed desirable to determine whether in addition to this 

 physical reversibility there was also complete physiological reversi- 

 bility in the sense of permitting normal development to occur after 

 solidification had been brought about. To test this point, a suspen- 

 sion of sperm was added to various lots of eggs after the CO 2 had 

 been allowed to evaporate and the eggs had regained their fluidity. 

 The results of these experiments were somewhat conflicting. In 

 some cases no development occurred, in others there was cleavage 

 as far as the 4- or the 8-cell stage, with perhaps irregular develop- 

 ment beyond that point, while in still others normal development 

 was obtained. The probable explanation of these differences was 

 soon found to be that the exposure to CO 2 caused membrane for- 

 mation (as had been noted by a number of previous observers) 

 and subsequent development depended on whether or not condi- 

 tions were favorable for complete artificial parthenogenesis. But 

 whatever may have been the factors concerned in bringing about 

 development, the mere fact that it occurred even in a portion of 

 the cases where the eggs had undergone a very noticeable solidifi- 

 cation is definite proof of the possibility of physiological reversi- 

 bility. 



It will be noticed that there have been described no liquefaction 

 effects on Arbacia eggs. Whether or not such effects can be pro- 

 duced by lower concentrations or shorter exposures or both can be 

 determined only when suitable material is- again available. The 

 experiments here described were made with another end in view 

 before conditions in Paramcecium and Colpidimn had been investi- 

 gated, and the possibility of a preliminary liquefaction before 

 solidification was not suspected. Though the experiments are, 

 therefore, to this extent incomplete, their results, as far as they go, 

 are in agreement with those obtained with the other kinds of 

 material studied. 



EXPERIMENTS ON AMCEBA. 



The possibility of producing definite changes in the consistency 

 of protoplasm by means of CXX suggested an interesting applica- 



