BIPARENTAL INHERITANCE IN PARAMECIUM 459 



A method of analysis for determining whether this is correct 

 was worked out, and is described in Part I. Analyzing in this 

 way the data from a large number of experiments performed 

 partly by the present authors, partly by Miss Cull ('07), the 

 following is found: 



1. As to survival and death, the fate of the two members of a 

 pair is more ahke, not less alike, than would be expected if the 

 distribution of deaths has no relation to the pairing. If one mem- 

 ber of a pair survives, the other member tends to survive also; 

 if one dies out, the other tends to die out also. Thus conjugation 

 has the effect of making the progeny of the two members resemble 

 each other in vitality. 



This effect of conjugation is very decided, so that the number 

 of pairs in which both members survive is much greater than would 

 be the case if the distribution of deaths and survivals were inde- 

 pendent of the pairing. 



The fact that this likeness in vitality is a consequence of con- 

 jugation, and does not exist before it, was shown by an extensive 

 experiment (Experiment 17) with 239 split pairs. The two pros- 

 pective members, separated before conjugation occurs, show no 

 such strong tendency to likeness in fate as is shown by the two 

 that have conjugated. 



2. As to the rate of reproduction, the two members of a pair 

 are more alike, not less alike, in their rate of reproduction, than 

 would be the case if the variations in reproductive vigor are dis- 

 tributed independently of the pairing. Thus conjugation has the 

 effect of making the progeny of the two members alike in their repro- 

 ductive power. 



Thus these relations give no evidence for sexuality considered 

 as a tendenc}^ for the two members of a pair to be diverse in vital- 

 ity and reproductive power; the condition actuall}^ existing is the 

 reverse one. 



What they show is that biparental inheritance occurs as a result 

 of conjugation, the vitality and rate of reproduction being affected 

 by both parents, so that the progeny of the two resemble each 

 other in these respects. • 



