CAGED NORWAY 385 



be remembered that the domestication of the Norway has been 

 carried on by Dr. King for only a few generations, and at the 

 moment it is but the F 9 which is under observation. Many of 

 the statements to be made in this paragraph probably apply to the 

 wild Norway also, but the full application of them must await 

 further observations. Domesticated Norways become progress- 

 ively less timid and easier to handle. They still gnaw their cages. 

 The growth curve which in the early generations lags behind that 

 of the Albino up to maturity tends in later generations to become 

 more like that of the Albino. The time of suckling thus far 

 continues somewhat longer in the Norway and the time of breed- 

 ing, which in the earliest generations was at seven or eight months, 

 appears earlier. The number of litters tends to be less than in the 

 Albino, but the number of young per litter is about the same. 

 The sex ratio is very low. The eyes open at 1 7 days. 



Caging and domestication increase the body weight, but reduce 

 the weight of the brain and spinal cord and the weights of the 

 suprarenals and gonads. The hypophysis and thyroid are not 

 conspicuously modified. 



(c) Characters which in the Albino given exercise tend to return 

 to the Norway type. Turning out Albinos to live the wild life in 

 hopes that the descendents might be later examined, after a 

 series of generations, has not been successful, though tried in 

 several places. The liberated Albinos fail to establish themselves. 

 In view of this result it has seemed best to try the effect of one of 

 the elements of the wild life, namely, exercise. 



When Albinos are permitted to exercise in a revolving cage 

 within a single lifetime, the weight length relations become 

 similar to those of the wild Norway. The percentage weight 

 of the musculature increases. The brain increases slightly in 

 weight, but there is no clear change in the weight of the spinal 

 cord. The percentage of water in both of these parts is however 

 slightly increased. The suprarenals and gonads are increased 

 hi weight, while the hypophysis tends to the relations found in the 

 wild Norway. The viscera, except the spleen, are also increased 

 in weight. 



