310 H. S. JENNINGS 



A watch glass culture of the race k showed on March 4 the 

 beginnings of conjugation, many of the individuals being observed 

 in the act of uniting; (for the history of the race before and after 

 this time, see the diagram, fig. 1). Three pairs were separated 

 as they were beginning conjugation; the component individuals 

 of these three split pairs were called 1, a and b; 2, a and b; 3, 

 a and b. Three other pairs, designated 6, 7 and 8, were allowed 

 to finish conjugation, then their members {a and b) were isolated 

 and cultivated on slides side by side with the others. Thus we 

 have six lines that have just conjugated; six others that were 

 attempting to conjugate, but were prevented. 



The experiment may be divided into three stages. The first 

 stage is from March 6 until April 1 1 (37 days) . (Those that had 

 conjugated did not divide until March 6, so that the fissions of 

 those that had not conjugated are counted, for comparison only, 

 from that day also.) 



All the six lines of those not allowed to conjugate lived and 

 multiplied vigorously throughout this period of five weeks and 

 two days. Of the six lines derived from those that had conju- 

 gated, on the other hand, four died out completely within two 

 weeks, while the others multiplied more slowly than did those 

 that had not conjugated. The detailed records for the 12 lines 

 are given in table 13. Here the classification by weeks begins 

 March 8, so as to omit in the weekly record the irregularities 

 due to the first two or three days after conjugation; this gives 

 us just five weeks. 



As table 13 shows, even the two lines of conjugants that li\'ed 

 multiplied less rapidly than did those that had not conjugated, 

 the weekly average for all the former being 8.8, while for the 

 latter it is 10.2. The next stage of the experiment was of a 

 character to determine whether this difference in rate of fission 

 continues beyond five weeks, as well as to decide whether it 

 might be due to accidental causes, or was a result of inherent 

 differences. Of the non-conjugants, the pairs 1 and 3 were con- 

 tinued till April 12 (31 days additional), while the conjugants were 

 represented by 7 a only. Several lines of each set were kept in 

 progress. The results are given in table 14 for two periods of 



