The Life History of TiUina Magna 401 



generations, and Woodruff watched Oxytricha fallax through 

 860 generations. On the other hand, conjugation has been 

 studied by Maupas in the case of Colpoda, which in form is closely 

 related to Tillina. There are two possible explanations of the 

 non-appearance of conjugation stages: the first, that the condi- 

 tions under which the experiments were carried out lacked the 

 proper stimulation for conjugation, the protoplasm never reaching 

 the miscible condition which Calkins described as characteristic 

 of conjugating paramecia; the second possibility is that Tillina 

 may be an intestinal parasite, and that the conjugation processes 

 are carried on under very different surroundings from that in 

 which the normal simple division takes place. The fact that the 

 main stock was lost or disappeared from the culture jar, in which 

 they were originally abundant, is the reason that I was not able 

 to experiment with large numbers of wild material. 



VI OBSERVATIONS ON THE LIFE HISTORY 



The A culture, consisting of four individual lines of the same 

 ancestry (Al, A2, A3, A4) was started on November 7, 1906, and 

 died on March i, after having passed through 210 generations. 

 Diagram II was made according to the methods of Calkins. The 

 curve represents the average number of divisions per day, of each 

 individual for ten-day periods, thus representing as a whole, 

 the division energy or general vitality of the protoplasm of the 

 A culture. 



The curve is similar to those already made for Paramecium 

 and Oxytricha. There are the same periodic rises and falls in the 

 division rate which Woodruff has termed the "rhythms." The 

 curve is a normal one with the exception of the unusual decrease 

 in the division rate at the fifth period. This, however, is explained 

 by the fact that an unexpected fall in the temperature of the lab- 

 oratory took place during the Christmas holidays, and during 

 this period many encysted permanently, and all of the lines suf- 

 fered a marked decrease in vitality. Aside from this exception, 

 there is a gradual downward tendency in the curve, indicating 

 a general decrease in the vitality, and marking the approach of 



