LIFE PROCESSES IN CAPTIVE GRAY RATS 



the relative growth rate of the sexes during the suckling 

 period. Such data are now available, since a recent paper 

 (King, '35) gives birth weights for 6295 gray rats taken 

 mainly from later generations. These records give the aver- 

 age weight of 3228 males as 5.5 gm., and that of 3067 females 



TABLE 1 



Increase in the weight of the body with age for individuals in the eleventh to the 

 fifteenth generation of captive gray rats 



as 5.2 gm. (King, '35). Thus at birth the body weight of gray 

 males exceeds that of females by 0.3 gm. (5.5 per cent). 



Taking these weights as norms, it is shown by data in table 

 1 that in the eleventh to the fifteenth generations the sexes 

 were growing at approximately the same rate when 13 days 

 of age. At 30 days, however, the weight difference of 2 gm. 

 (4.5 per cent) indicates that females were then growing more 



