LIFE PROCESSES IN CAPTIVE GRAY RATS 13 



males attained an average weight of 362 gm. Graph B, for 

 males of the twenty-fifth generation, rises rapidly and does 

 not tend to flatten until the age period of about 150 days, thus 

 indicating a marked growth acceleration during adolescence 

 and early maturity. The variance in the levels of graphs A 

 and B during the period of 60 to 150 days indicates a weight 

 difference between these two groups of males of some 35 per 

 cent. At subsequent age periods the graphs run nearly 



Males 



Body weight In grams 



250 



A Generation 1 



B Generation 25 

 / S 



150 



Aga in days 



Fig. 3 Body growth in males of the first and of the twenty-fifth generation. 



parallel, but at levels indicating that males of the last genera- 

 tion were about 20 per cent heavier than those of the first 

 generation during the greater part of adult life, and 17 per 

 cent heavier at the final weighing when their average weight 

 was 440 gm. 



Data from table 6 were used in constructing the growth 

 graphs for females of the first and of the twenty-fifth genera- 

 tion, which are shown in figure 4. 



The graphs in figure 4 run more irregularly than do those 

 in figure 3, because the effects of early pregnancy and of 



