366 H. S. JENNINGS 



inherited differences. But working with a pure race, as in 

 Experiments 13 and 15, it is found (1) that differences in rate of 

 fission among those that have not conjugated since they were 

 derived from a single parent are not inherited (unless possibly 

 certain differences of a minimal character are to be excepted; 

 differences of an order of magnitude far below those with which 

 we are dealing) ; (2) that conjugation among the members of such 

 a pure race does result in differentiations that are inherited, so 

 that from a race homogeneous with respect to fission rafte, we 

 get many races, differing in their rates. The hereditary dif- 

 ferences thus produced are not small and inconstant but so decided 

 as to give coefficients of correlation up to 0.9 between earlier and 

 later generations, in spite of fluctuations due to environmental 

 differences. 



To what is due the production of inherited differentiations by 

 conj ugation? Here for the present we can only speculate. It would 

 seem probable that we have before us something of the process that 

 we see in Mendelian inheritance. If the members of a culture 

 differ in their germinal make-up, conjugation among them would 

 produce many new combinations of germinal characteristics. 

 The fact that we find such heritable differentiations produced by 

 conjugation among the members of the same pure race would be 

 accounted for if the members of the race are heterozygotic, 

 although all alike in germinal composition. Interconj ugation 

 among such similar heterozygotes would, on Mendelian principles, 

 produce many new combinations of germinal constituents, just 

 as happens in the self-fertilization of higher organisms. 



In connection with such a view of the matter, it needs to be 

 recalled, however, that in our Experiment 13 we were dealing 

 with a stock that had gone through eight successive self-fertili- 

 zations, the stock being derived, after each of these, from a single 

 ex-conjugant. Such a series of eight self-fertilizations would, as 

 set forth in the account of Experiment 13, go far in getting rid of 

 heterozygotism, unless the character we are studying depends on 

 a very large number of independent factors. In that stock we 

 nevertheless found that inherited differentiations as to fission rate 

 were produced by conjugation. This may indicate that Men- 



