124 



Scientific Proceedings (29). 



78 (334) 

 The life cycle of Paramecium. 



By LORANDE LOSS WOODRUFF. 



\From the Sheffield Biological Laboratory of Yale University.'] 



On May I, 1907, a culture of Paramedian aurelia (caudatum) 

 was started with a "wild" individual from a laboratory aquarium, 

 and since that time up to the present (May 20, 1908) it has been 

 under daily observation. Hay infusion was employed as a culture 

 medium during the first few months of the life of the culture, but 

 later the culture medium has been constantly varied by employing 

 water from different sources and to this water has been added any 

 material which might be encountered in the natural habitat of Para- 

 mecium. In every case precautions have been taken to sterilize the 

 infusion before using it in order to obviate the possibility of con- 

 taminating the culture by introducing a live cyst of a "wild" 

 Paramecium. Conjugation has not been possible in the direct line 

 of the culture because the individuals of the culture have been 

 isolated almost daily. 



Under these conditions the culture has so far attained 490 gen- 

 erations. During the greater part of the year the average rate of 

 division of the culture has been between one and two divisions 

 per day, and not during a single ten-day period has it averaged as 

 low as one division in two days. Thus no period of marked phys- 

 iological depression has been indicated by the division rate, and 

 no special stimuli have been found necessary to save the culture 

 from extinction. 



The results obtained up to the present time show that the life 

 cycle of Paramecium, when subjected to a varied environment, 

 may be much longer in duration of time and may comprise many 

 more generations than when subjected to a constant culture me- 

 dium of hay infusion, as has been the case in previous investiga- 

 tions in this field. 



