II. SIZE OF THE BODY AND ORGANS 



75 



for both sexes have the same trend, except at G 10 . 



G 3 and G 10 the maximum difference is about 6 per cent in 



both sexes. 



At GI the age of the group is high and at G 2 it is low in 

 both sexes as compared with the subsequent age values. As 

 would be expected, the older group, G!, has a greater length 

 and the younger, G 2 , a lesser length. There is a markedly 

 low length at G 5 , and, as later observations will show, this is 

 probably a retardation in growth in response to unfavorable 

 conditions acting on this generation. As the data stand, 

 there is no significant difference at 600 days between the 

 body length at G 3 and at G 10 , so that there is no evidence that 

 the captive Grays have undergone a progressive change in 

 body length on age during this period. 



TABLE 11 



General data on the number, age, body length, and body weight of the gray 

 Norway rats used for this study and the deviations of the observed body weight 

 from the body weight as given in the reference table 187 (The Bat, 'S4) for 

 the observed body length. Charts 12 and IS. Males 



