HELEN DEAN KING AND HENRY H. DONALDSON 



In each of the generation groups the percentage differences 

 in the average body weights of males and females remained 

 fairly constant throughout adult life, the variation being but 

 2 per cent in the first two groups and 4 per cent in the third 

 group. These differences tended to decrease, however, as the 



TABLE 2 



Showing the increase in the weight of the body with age for individuals in the 

 fifth to the seventh generations of captive gray rats 



generations advanced. The male excess in weight in the 

 third group was 7.9 per cent lower than that in the first group 

 when the animals were 182 days of age, and 6.4 per cent less 

 when the maximum was reached at 578 days. This progres- 

 sive lessening in the percentage differences between the body 

 weights of males and females was due, as a comparison of the 



