346 S. O. MAST 



encystment or conjugation had occurred in them. And since 

 these groups all originated in the same individual and were 

 carried along parallel with each other and treated alike, it is 

 obvious that the rate of fission ought to differ in them if conju- 

 gation or encystment has any effect on it. 



The detailed description, given above, of the earlier periods 

 shows that if conjugation had any effect on the rate of fission 

 during these periods it was a retarding effect which, however, 

 continued for but a short time after conjugation. An examina- 

 tion of the table shows that the same may be said regarding 

 all of the other periods. It shows also that encystment has no 

 appreciable effect on the rate of fission. Take for example, the 

 five day period (9/22-9/26, 1911) or better still, the twenty day 

 period (9/7-9/26, 1911); here we find that the seven groups of 

 lines produced during this period the following average num- 

 ber of generations respectively: 76, 75, 74, 74f, 76, 73, 75f, a 

 maximum difference of only three divisions in twenty days, 

 while the number of generations since conjugation had occurred 

 in these groups of lines varied from 118 to 524 and the number 

 of generations since encystment from 75 to 236. Moreover, the 

 rate of fission is not greatest in the groups in which the period 

 considered is nearest the point of conjugation and encystment or 

 least in those in which it is farthest from these points. 



The sixty day period immediately following (6/1-7/30, 1912) 

 shows even a more striking similarity in the rate of fission in lines 

 which have conjugated compared with those which have not. 

 Here we find that a group of lines in the sixty days immediately 

 after conjugation produced an average of 248 generations and 

 that during the same period lines from the same stock but in 

 which conjugation was prevented produced an average of 249| 

 generations. Again, near the close of the experiment we find 

 that in a twenty day period (5/9-5/29, 1913) lines immediately 

 after conjugation produced 32 generations, while the stock 

 from which they were isolated, after having passed through over 

 1,500 generations without conjugation, produced in the same 

 period and under identical conditions, 33f generations. There is 

 consequently no evidence whatever indicating that conjuga- 



