(31) 



The new conflicting results, like previous ones, can still 

 be explained away as due to complicating factors. For ex- 

 ample, the inheritance of abnormalities in Paramecium 

 (Stocking 1915) can be considered to follow from an abnor- 

 mal condition of the macro-nucleus; the inheritance of 

 variations in fission-rate in Stylonychia (Middleton 1915) 

 might be due to the accumulation of waste products in the 

 cytoplasm of the slowly-dividing, large-sized group. And 

 in Difflugia and Centropyxis (Jennings 1916 and the present 

 paper), xxntil we know more about the process of cell di- 

 vision in these organisms, the observed inheritance of 

 variations can be explained by the assumption that a pro- 

 cess of somatic segregation or fractionation of the chro- 

 midial body takes place at each cell division, as has been 

 suggested by Morgan (1916, p. 185) . Other similar cases 

 could doubtless be supplied with other explanations along 

 the same lines. 



But there is another viewpoint, alternative to the 

 first one, which seems to me to be preferable. According 

 to this idea, one may assert that the pure line concept is 

 correct on the average, only; that it is a mathematically 

 correct expression of the mean result of inheritance under 

 natural conditions. But, just as the Galton-Pearson lav/ 

 of ancestral inheritance, though accurate mathematically, 

 does not fit the details of Mendelian heredity, on the 

 average result of which it is presumably based, so the 

 pure line hypothesis, though true for average results, 

 may be thought of as not holding in ihdividual cases. 



