EFFECT OF CONJUGATION 315 



Eight lines descended from these conjugants of April 9 (branch 

 B) were kept under observation till April 30. As the first fission 

 did not occur till April 12, this gives nineteen days during which 

 the rate of fission was determined for these. Of the non-con ju- 

 gants of ]\Iarch 4 (branch A, fig. 1), fifteen lines were in progress 

 at this time. 



The average number of fissions for the nineteen days was, in 

 the conjugants of branch B, 21.375, while the average rate of 

 fission was 1.125 per day. In the non-conjugants of branch A, 

 the average number of fissions for nineteen days was 21.533, the 

 daily rate 1.133. 



There was thus no appreciable difference in rate of fission. 

 The branch A shows no sign of injury as a result of having 

 omitted several conjugations which the branch B has undergone. 



Experiment 9: April 29 to June 7, 1910: Paramecium aurelia 



On April 29 there was another conjugation in branch B (9, fig. 1) 

 in the same direct line as the conjugations of Experiments 7 and 8. 

 That is, the conjugants of our present experiment are all descended 

 frorn a single ex-conjugant of Experiment 8, these from a single 

 ex-conjugant of Experiment 7, and so on. Thus there have now 

 been in this branch B three conjugations (probably four), since 

 there has been a conjugation in branch A. The members of 

 branch A have been cultivated on slides since March 4, while 

 those of branch B have been cultivated part of the time on slides, 

 part of the time in watch glasses. 



Precise comparison of branch A (fig. 1) with the progeny of one 

 of the ex-conjugants of April 29 in branch B was not made till 

 about two weeks after the conjugation of the latter. During this 

 time observation with the eye seemed to indicate that the mem- 

 bers of B were a little larger than those oi A. In view of this 

 apparent differentiation between the two, experiments were set 

 on foot for comparing the fission rate and the dimensions. 



Fission rate. Four separate series or lines of propagation were 

 carried on from May 22 to June 7, both for the conjugants {B) and 

 the non-conjugants {A). 



