LIFE PROCESSES IN CAPTIVE GRAY RATS 



23 



variability in females of the twenty-fifth generation was sig- 

 nificantly less than that in females of the first generation. 



A correlation between body-weight variability and the 

 growth rate in both sexes of gray rats is indicated by the fact 

 that in all generation groups of males (table 5) and in the 

 last two generation groups of females (table 6) variability 

 was at its maximum when the rats were young and growing 



v-- 



GC IN MONTHS 



Pig. 6 Body-weight variability with age in the first and in the twenty-fifth 

 generation. 



rapidly, and then decreased as the growth rate declined dur- 

 ing adult life. A similar correlation has been found in the 

 albino rat (King, '15), in the mouse (Robertson, '16; Sailer, 

 '27; Kopec, '32), as well as in man (Boas and Wissler, '05). 

 There is no sex difference in body-weight variability at 

 birth in gray rats. Coefficients of variation, calculated from 

 a large series of birth weights (King, '35) give for males a 

 value of 13.7 0.11, and for females 13.6 0.12. Compari- 

 son of corresponding coefficients in tables 5 and 6 and the 



