EFFECT OF CONJUGATION 295 



bers. The culture fluid was changed as a rule every other 

 day. 



Since usually members of pairs of conjugants do not divide till 

 the second day after conjugation, the comparison of the rate 

 of fission for the three sets was not begun till this second day. 

 Thus, the animals were isolated on the morning of April 8, but 

 the tabulation of the fissions begins, for all sets, on April 10. 



For purposes of comparison, the fissions were tabulated by 

 weeks for each of the three sets. The experiment may best be 

 divided into two periods, the first comprising the first two weeks; 

 the second the last six weeks. At the end of the second week a 

 considerable number of each set were lost by accident, so that 

 the number to be dealt with is much smaller in the second period. 



The experiment included at the beginning 57 lines (28^ pairs) 

 of those that had finished conjugation; 39 lines (19| pairs) of 

 split pairs, and 58 lines of 'free' individuals. 



The actual number of fissions per week is given for the first 

 two weeks in table 30 ; for the last six weeks in table 31 (Appendix) . 



It should be noted that the data given are, so far as numbers 

 of fissions go, of little value after the sixth week, and particularly 

 is this the case for the seventh week. Pressure of other duties 

 forced me to neglect these experiments at that time, so that 

 during the seventh week the slides were changed but once; as a 

 result they hardly multiplied at all. The figures for the seventh 

 and eighth weeks are given only in order not to suppress any 

 part of the record. 



It is evident, as in the previous experiment, that the animals 

 which were ready for conjugation were by no means in a de- 

 pressed or degenerate condition. The split pairs continue to 

 multiply, somewhat more rapidly than those that have conju- 

 gated. We shall examine in detail the rate of fission, the varia- 

 tion, and the mortality, in the three sets. 



Rate of fission. Table 6 gives the mean numbers of fissions 

 in each set, for each week, and for certain other periods. 



As this table shows, in practically all of the 15 means given, 

 the rate of fission is less for those that have conjugated than for 

 those that have not. The only exception is in the seventh 



THE JOUHNAI, OF EXPERIMENTAL ZOOLOGY, VOL. 14, NO. 3 



