94 HELEN DEAN KING 



ability in body weight than had the females. Coefficients of 

 variability for the body weights of the individuals in the earlier 

 generations of the inbred strain (King, '18; table 15), and also 

 those for various series of stock Albinos (Jackson, '13; King, '15), 

 all show that the males are more variable than the females. Such 

 a relation between the sexes as regards the variability in their 

 body weights would seem to be a characteristic of the albino 

 strain of rats in general, and from the results obtained in the 

 present study it is evident that this relation has not been changed 

 by twenty-five generations of close inbreeding. 



Males in the sixteenth to the twenty-fifth generations of the 

 A series of inbreds had a somewhat greater range of variability 

 in body weight than had the males of the B series, judging from 

 the relative size of the coefficients for the two series as given in 

 table 12. Between the average coefficients for the two series 

 there is a difference of 1.6 points in favor of the males of the 

 A series ; a similar relation between the two series existed also at 

 an earher period (King, '18; table 15). Throughout all genera- 

 tions of the inbred strain, therefore, the range of variability 

 in body weights was greater in the males of the A series than in 

 those of the B series. This difference persisted even during the 

 periods when body growth and variability were greatly influ- 

 enced by environmental and nutritive conditions. 



A comparison between corresponding coefficients for the fe- 

 males of the two inbred series (table 12) shows that, as a rule, 

 the females of the A series were sUghtly more variable in body 

 weight at different age periods than were the females of the B 

 series, but, taken as a whole, the one group of females was about 

 as variable as the other, since the difference between the average 

 coefficients for the two groups is only 0.7 point. As the study 

 of variabihty in the females of the earlier generations of the 

 inbred strain led to the conclusion that "the range of variability 

 in body weights was practically the same for the females of the 

 two inbred series," it is evident that long-continued inbreeding 

 has not altered the relative variability of the females in the two 

 inbred series any more than it has that of the males. 



