STUDIES ON THE LIFE CYCLE OF PARAMECIUM. 307 



still in captivity give every indication of being in as normal phys- 

 iological and morphological condition as their ancestor. This 

 suggests that when the protoplasm is constantly subjected to a 

 suitable varied environment the cycle may be greatly prolonged 

 and probably entirely eliminated the fluctuations in vitality not 

 transcending the rhythm. 



SHEFFIELD BIOLOGICAL LABORATORY, 

 YALE UNIVERSITY. 



LITERATURE. 

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