458 H. S. JENNINGS AND K. S. LASHLEY 



alike in respect to the character studied; yet from some pairs the 

 progeny had a high rate of fission, others a low one. But all 

 recent work has emphasized the fact that the limiting of the con- 

 cept of inheritance to resemblance is purely artificial; the pro- 

 geny often inherit from a parent something which makes them 

 quite unlike the parent. In the present case it appears clear that 

 both parents do affect both sets of progeny, otherwise the latter 

 would not be alike; it appears proper therefore to speak of this as 

 biparental inheritance. 



To fit the results in this case to any scheme of inheritance known 

 for other organisms appears difficult. This is the first demonstra- 

 tion of biparental inheritance in cases where the two cells that 

 conjugate both continue to exist and reproduce. If the two par- 

 ents were ordinary heterozygotes, alike in their germinal charac- 

 ters, it does not appear clear why the two sets of progeny should 

 resemble one another so closely. One might expect that they 

 would often receive different combinations of germ plasm. But 

 it is not worth while to speculate on this aspect of the matter till 

 the facts are better known. An experiment with larger numbers 

 of pairs and split pairs, derived from a single individual, would 

 help greatly in the' interpretation. But the fact of biparental 

 inheritance in the conjugation of infusoria is clearly established 

 by the present results. 



GENERAL SUMMARY 



After conjugation in Paramecium, usually a considerable 

 number of the lines of progeny descended from the conjugants 

 die out or are weak. 



Since in many of these cases the lines descended from the two 

 members of a pair differ in their fate, one dying or reproducing 

 slowly, while the other lives and reproduces vigorously, it has 

 been held that this indicates an incipient sexuality — the 'male' 

 reproducing little or not at all, the 'female' reproducing vigor- 

 ously. The two members of the pair were thus held to be less alike 

 in their vitality and reproductive power than would be the case 

 if the deaths and the variations in reproductive power were dis- 

 tributed without reference to the pairing. 



