24 HELEN DEAN KING 



tions (graph D), the body increase with age was about the same 

 in all the various generation groups of inbred females up to the 

 time that the animals were one year old. After this age the 

 females in the group comprising the seventh to the ninth genera- 

 tions were somewhat heavier than the other females, but their 

 excess in body weight was very much less than that in the cor- 

 responding groups of males (fig. 6). 



On referring to the data in table 4 to table 7 it is found that 

 in both series of inbreds the average body weights of the animals 

 in the seventh, eighth and ninth generations were greater than 

 those of animals in the tenth and subsequent generations. In 

 the seventh generation, particularly, females as well as males 

 were exceptionally heavy animals at all ages for which records 

 were taken. The largest males yet obtained belonged in the 

 seventh generation of the A series of inbreds ; these rats weighed 

 at their maximum 460, 482, and 511 grams respectively. The 

 largest female in the series was a member of the seventh genera- 

 tion of the B series of inbreds, and she weighed 323 grams when 

 she was 425 days old. The probable cause for the unusual 

 weight of the animals in the seventh to the ninth inbred genera- 

 tions will be considered later. 



Data showing the range in variation and the averages for the 

 body weights at different ages of the weighed individuals in the 

 A series of inbreds (seventh to fifteenth generations only) are 

 given in table 11. Similar data for the rats of the B series are 

 shown in table 12. 



The graphs in figure 8 were drawn to show the relative growth 

 in body weight of the males belonging to the two inbred series 

 (data in table 11 and in table 12). 



The males of the B series of inbreds had a heavier average 

 body weight than the males of the A series up to the last weigh- 

 ing period (455 days), as the position of the graphs in figure 8 

 show. The crossing of the graphs at the end has no significance, 

 since the largest males of the B series died before the final 

 weighing. 



Graphs showing the growth in body weight of the females in 

 the two inbred series are shown in figure 9: the data for these 

 graphs are given in table 11 and in table 12. 



