EFFECT OF CONJUGATION 317 



TABLE 17 



Experiment 9. Paramecium aurelia. Comparative lengths in microns of A andB. 

 These belong to the same pure strain, but A has been cultivated for a long time 

 without conjugation, while B has conjugated at least three times in succession 

 since A. 



May 19 : age, 30 minutes . 

 May 22: adults, ill fed... 

 May 2S: adults, well fed. 

 June 1: adults 



No. Mean length 



No. I Mean length 



116.600 ±0.551 

 99.000 ± 1.195 

 641135.469 =fc 1.042 

 65131.877 ±0.616 



11125.454 ± 1.063 

 50|l23.680± 0.913 

 70141.429 ±0.785 

 4l|l32.237± 0.747 



line k. However, the fact that the difference was so extremely 

 small at the last measurement taken admonishes us not to lay 

 too much stress upon this case; the matter must be tested further. 



Determination of co7ijugation. With A and B (fig. 1) a study 

 was made as to the relative influence of external and internal con- 

 ditions in inducing conjugation. In B, as we have seen, there 

 had been at least four successive conjugations since there has 

 been one in A. Will A be therefore readier to conjugate than B? 

 If conjugation depends mainly upon an internal condition of need, 

 then certainly we should expect this. 



To test this, watch glasses of A and B were set side by side 

 May 13, two weeks after the last conjugation of B, and the con- 

 ditions for inducing conjugation supplied, so far as possible. 

 On June 3 conjugation occurred in both A and B. 



Thus under the proper conditions both sets conjugate at the 

 same time, in spite of the fact that one has conjugated at least 

 four times since the other. The experiment indicates that the 

 recent external conditions are of more importance in determining 

 conjugation than a progresive internal need arising through the 

 fact that conjugation has not lately occurred. 



Experiment 10: May 10 to May 20, 1910: Paramecium aurelia 



On May 10 there was a conjugation in branch C (fig. 1, page 

 307), making the third in series in this division since any conju- 

 gation occurred in A. Four pairs were isolated from this new 

 conjugation in branch C, and experiments were set on foot for 



