394 H. S. JENNINGS AND K. S. LASHLEY 



PART III. By H. S. Jennings 451 



Conjugation within a pure strain: Experiment 15 451 



Summary 457 



General summary 458 



Literature cited 460 



Appendix: 



Formulae used in the analysis 461 



Table 51 463 



PART I 



H. S. JENNINGS 

 INTRODUCTION 



When the individuals of Paramecium that have paired are 

 kept separate and allowed to reproduce under favorable conditions, 

 as a rule a considerable number of the lines of progeny produced 

 by them either die out, or reproduce very slowly; while the others 

 live and reproduce freely. This has been studied by Calkins 

 ('02) and by Cull ('07) and is held by them to indicate that there 

 is at least an incipient sexuality in Paramecium. Of the two 

 members, a and h, of a pair, one is held to reproduce freely, thus 

 corresponding to the female, while the other, reproducing little 

 or not at all after conjugation, represents the male. Since the 

 life of individuals that do not reproduce is short, the 'males' will 

 in many cases die in a brief period after conjugation. 



METHOD OF ANALYSIS: FORMULAE 



Now, of course the mere fact, in itself, that a considerable 

 number of the lines of progeny are weak or die out after conjuga- 

 tion does not show that there is a tendenc}^ to sexual differentia- 

 tion in the members of pairs. There might be causes of weakness 

 or death that are quite independent of such sexual differentiation. 

 How can we determine whether the observed cases of weakness 

 and death do indicate a sexual differentiation? 



For answering this question the following considerations apply : 

 If the causes of death are quite independent of sexual differentia- 

 tion between the two members of the pairs, then sometimes both 

 members of a given pair will die or be weak, and it should be pos- 



