460 H. S. JENNINGS AND K. S. LASHLEY 



Biparental inheritance in rate of reproduction was tested by 

 an extensive study of the coefficient of correlation between the 

 numbers of fissions in the descendants of the two members, for 

 given periods. A decided positive correlation was found, ranging 

 usually at about 0.3 to 0.4, but rising as high as 0.9, in the case of 

 conjugation among the progeny of a pure race. 



In the case of mixed cultures it was found that there is a slight 

 and varying degree of correlation due to assortative mating, so 

 that it is shown by the progeny of members of split pairs. Thus 

 assortative mating occurs with reference to reproductive vigor; this 

 is probably a secondary consequence of the assortative mating 

 based on size, which was previously known to exist. 



But this correlation is increased by conjugation; showing that 

 conjugation produces biparental inheritance. 



Demonstration of this is most strildng in the case of conjuga- 

 tion among the descendants of a single individual (a 'pure strain'). 

 Here there is no assortative mating with respect to fission rate; 

 all the individuals having before conjugation the same. rate. 

 There is thus no correlation in fission rate for the members of 

 split pairs. 



But after conjugation there is a differentiation as to fission 

 rate among the pairs, and the two members of a given pair show 

 a most striking correspondence in rate. The coefficient of corre- 

 lation rises in such cases to 0.9. 



Thus biparental inheritance is (for the first time) demonstrated 

 to exist as a result of conjugation in infusoria. 



LITERATURE CITED 



Calkins, G. N. 1902 Studies on the life-history of Protozoa. I. The life-cycle 



of ParamcEcium caudatuin. Arch, of Entw.-mech., Bd. 15, pp. 139-186. 

 Cull, S. W. 1907 Rejuvenescence as the result of conjugation. Jour. Exp. 



Zool., vol. 4, pp. 85-89. 

 Degen, C. F. 1824 Tabularum ad faciliorem probabilitatis computationem 



utilem Enneas. Copenhagen. 

 De Morgan, A. 1845 Article on 'Probabilities,' Encyclopedia Aletropolitana, 



vol. 2. 

 IlARFtis, J. A. 1909 A short method of calculating the coefficient of correlation 



in the case of integral variates. Biometrika, vol. 7, pp. 215-218. 



