660 



ENDOMIXIS 



Laboratory, whenever tests have been made; but now, in the thirty- 

 third year of its Hfe, with unimpaired vitaHty, the interendomictic 

 periods seem to be shghtly more variable in length (Fig. 164), 



A number of other investigators have studied the question of peri- 

 odicity in this and other races of P. aurelia and P. caudatum, among them 

 R. T. Young (1918), JoUos (1916, 1920), Erdmann (1920), Chejfec 

 (1930), Galadjieff (1932), and, in particular, Sonneborn (1937a). 



Figure 164. Graph of the division rate of Paramecium aurelia, line III, subculture IE, 

 averaged for five-day periods. Endomixis occurred during the periods indicated by an X. 

 Note that the interendomictic periods exhibit some variation in length, and the final 

 endomixis shown is deferred. (From Woodruff and Erdmann, 1914.) 



The latter compared the endomictic period in the Yale race of 

 P. aurelia with that of another race under identical environmental condi- 

 tions. Sonneborn shows that great variations may exist in the interendo- 

 mictic interval, not only in different races, but even in the same race under 

 carefully standardized conditions of daily isolation culture. 



So in regard to the periodicity of endomixis, it now appears that the 

 limits of approximately 25 to 30 days and 40 to 50 fissions for P. 

 aurelia, and 50 to 60 days and 80 to 100 fissions for P. caudatum, as 

 originally announced, are somewhat too narrow and stereotyped. En- 

 vironmental and racial factors play a still greater part than these investi- 

 gators believed. But withal, the endomictic process does reair with con- 

 siderable regularity when the environmental and genetic factors are 

 uniform, and so must still be regarded as periodic. 



Genetical Studies on Endomixis 



Genetical sthdies on endomixis include those by Erdmann (1920), 

 Jollos (1921), Parker (1927), Caldwell (1933), Kimball (1937, 

 1939), and Sonneborn (1937b, 1939a, 1939b, 1939c). The results 



