304 H. S. JENNINGS 



have been undertaken, but after two or three weeks of intense 

 labor, all representatives of this race k cultivated on the slides 

 have become unhealthy and died. Earlier in its history it was 

 kept on slides for months in succession, multiplying vigorouslj^ 

 throughout. Whether its present peculiarity in this respect has 

 any connection with the long continued inbreeding, or whether 

 it may be due only to weakening from previous long cultivation 

 on slides, it is difficult to say; there is some indication, as we shall 

 see, that the latter is the case. 



Experiment 4- October 19 to November 8, 1908: Paramecium 



aurelia 



The first experiment on conjugation in race k was designed 

 primarily to permit a comparison of the dimensions of the progeny 

 of conjugants and non-conjugants in the same race. The results 

 so far as dimensions are concerned are given in my paper of 1911 

 on Assortative mating (pp. 96-97). Incidentally, the records 

 kept give data as to the relative rate of fission, and as to mortality. 

 As we have noted above, in this experiment (alone of all those 

 with A:), the race is not yet known to be absolutely pure, in the 

 sense of derived from a single individual, without admixture from 

 others; it is, however, extremely homogeneous, and probably 

 quite pure, even at this time. 



The experiment was begun with 46 paired individuals (23 

 pairs), and 46 that were non-conjugants, derived from the same 

 culture. During the course of the experiments 4 of the conju- 

 gant and 8 of the non-con jugant lines were accidentally lost, 

 leaving 42 of the former and 38 of the latter. 



This was one of the earliest experiments of the sort that I 

 tried, and the mortality was very high, doubtless owing to inex- 

 perience in handling. Of the 42 lines derived from the conju- 

 gants, but 17 lived throughout the twenty days of the experiment, 

 while of the non-conjugants 18 lines lived through. The total 

 number of fissions for each of these 35 surviving lines is given in 

 table 10. 



For the 17 con jugant lines the mean number of fissions is 

 13.294 ± 0.670, with a standard deviation of 4.098 ± 0.474 and 



