224 GEORGE ALFRED BAITSELL- 



whom the degeneration was thought to be due to an inherent 

 condition of senescence. In these experiments, it can be said 

 that such was not the case, for 'sister cells' which were kept under 

 other conditions in the mass test tube culture were, as far as 

 could be told both by careful observation of the living animals 

 and a thorough study of the prepared specimens, normal at the 

 time when, and for some time after, the daily isolation cultures 

 had died out. In figure 5 is shown a typical example of the 

 animals present in the test tube culture at this time. This speci- 

 men was preserved February 15, which was several days after 

 the last of the daily isolation cultures had died. Figure 6 is 

 a specimen preserved from the test tube culture May 18 and 

 it shows an atypical condition of the nucleus and cytoplasm. 

 Before this time specunens preserved from this culture gave 

 every evidence of being in as normal condition as is shown in 

 figure 5. After this time, however, the number of abnormal 

 animals in the test tube culture rapidly increased, due, it is 

 believed, as in the daily isolation cultures of this organism, to 

 the cumulative effects of an environment not entirely adapted 

 to the organism studied, and subsequently (June 10, 1912) this 

 culture died. 



2. Pleurotricha lanceolata 



Figures 7 to 11 are from Pleurotricha lanceolata cultures. 

 In figure 7 is shown a typical normal individual. This specimen 

 was taken from the Ph culture soon after it was started. Figure 

 8 shows an animal taken from the same culture several months 

 later shortly before it died out. Another atypical specimen is 

 seen in figure 9 which was taken from the Pb culture at about 

 the same time. As in the Oxytricha fallax cultures so also 

 here in the Pleurotricha lanceolata cultures the changes which 

 appeared in the animals in the cultures that died out is shown 

 not to be due to 'senile degeneration' inasmuch as 'sister cells' 

 which were kept under other culture conditions do not show 

 simultaneous degenerative changes. Figure 10 is a typical nor- 

 mal specimen preserved from the Phtt culture some time after 



