GROWTH ON age: CAGED NORWAY 



343 



Albino rats are much heavier than these Norway rats during 

 adolescence and earl}^ maturity; in later life the body weights 

 of the Norways exceed those of the Albinos (charts 59 and 60), 

 and (King '23, chart 1, p. 85). 



TABLE 185 

 Data for eighteen litters ofFi N^onvay rats, showing the increase in the weight of the 



body with age 



It seems probable that the slow growth of the Norways during 

 early life is characteristic for the strain, and that the acceleration 

 in the growth of the Albinos is one of the results of domestication. 



Norway rats show a high degree of variability in body weight 

 at all age periods (table 186). In early life the females are 



