Internal Characteristics and Size 115 



stance, has been exerted upon a part of the popula- 

 tion. Jennings and Lashley ('13a) believed that the 

 ability to survive in cultures and the rate of reproduc- 

 tion by fission could be demonstrated to be inherited 

 from both parents. They found that the coefficients 

 of correlation between the two sets of progeny of a 

 pair were always greater than between other sets of ex- 

 conjugant lines "mated" at random. But the past per- 

 formances of the conjugant lines, before they paired, 

 were not known. 



Biparental size. With respect to the inheritance of 

 size in ex-conjugants there are data also upon Para- 

 mecium. Jennings and Lashley ('13b) compared the 

 variabilities in the dimensions of mates with the varia- 

 bilities among their progeny. Among the progeny of 

 43 pairs of individuals which had conjugated in wild 

 cultures, the body sizes were much more homogeneous 

 (after a lapse of 25 days since conjugation) than in the 

 two members of each pair. In the particular race stud- 

 ied, the coefficient of correlation for length between 

 mates was +0.39; this much was due to assortation in 

 mating. Between the two sets of progeny from each 

 conjugated pair, the coefficient of correlation was 

 +0.57. It seemed from this that the progeny of two 

 mates were more nearly alike than the mates them- 

 selves. This was interpreted to be due to the presence 

 of hereditary influences from both parents. But it 

 seems inadequate to compare in the case of the mating 

 parents the sizes of single individuals, and in the case 

 of the progeny the mean sizes based upon 16 to 66 in- 

 dividuals. It would be better to know the mean sizes 

 for many individuals in each of the parent lines before 

 conjugation occurred. For, all frequency curves of 

 size in Paramecium show that any one individual may 

 depart by 30 per cent or more from the mean length 

 which it represents genotypically. It may be recalled 



