332 H. S. JENNINGS 



• 



Thus, after eight self-fertihzations, more than 96 per cent of 

 the organisms would be homozygotic with respect to all ten 

 characters. 



Of course we do not know on how many independently heritable 

 characters depends the rate of fission (which was the character- 

 istic chiefly examined). If it depends on not more than 1€ such 

 characters, the chances are thus at least 26 to one that we are 

 dealing with a pure homozygotic organism, when we select a 

 single individual after the eighth successive self-fertilization of 

 the line. 



The above analysis is based on the view that there is no sepa- 

 ration of the zygotic constituents in the reproduction by fission, 

 this being indicated by the evidence thus far brought forward. 

 If it were not true, then we would expect the organisms consti- 

 tuting a pure strain (descended by fission from a single indi- 

 vidual) to become more and more diverse as fission was repeated, 

 for as any individual became homozygotic with respect to any 

 character it could produce forever after only progeny that were 

 homozygotic in that respect. The result would be in the course 

 of 20 or 30 generations to produce a set of individuals, each 

 of which was homozygotic with respect to all the characters it 

 bore, though the different ones would have diverse homozygotic 

 characters. Selection among such individuals would then give 

 rise readily to diverse races; this is opposed to the evidence 

 hitherto obtained. 



The eighth of the conjugations in succession took place April 29, 

 1910. A single ex-conjugant gave rise to a culture, which propa- 

 gated without admixture, till this experiment was begun, Decem- 

 ber 6, 1910. On the evening of December 5 a watch glass of the 

 animals was taken from the large culture; on the following 

 morning those in this watch glass were conjugating, while those 

 that remained in the large culture dish were not. 



Experiment 13 a. Fifty-two pairs were taken from the watch 

 glass, 100 non-conjugants from the culture dish; all these were 

 isolated on slides, in the way already described. Thirteen of the 

 pairs were later lost by an accident. This left 78 lines derived 

 from animals that had conjugated, 100 from animals that liad 



