COMPARISON WITH ALBINO 193 



These differences taken together indicate that the albino rat 

 has grown less well, and it seems most natural to attribute the 

 lack of growth to the whole set of conditions summed up in the 

 word 'domestication.' 



The most marked difference in structure thus far described 

 between the two forms is in the relative weight of the central 

 nervous system. That this is due to the effects of domestication 

 seems highly probable, in view of the observations of Darwin 

 ('83) and Lapicque and Girard ('07). 



There are still other observations which belong here. In a 

 study on the weight of some of the ductless glands of the Norway 

 and of the albino rat according to sex and variety Hatai, ('14 a) 

 an examination was made of the suprarenals, hypophysis, thy- 

 roid and gonads hi both forms. The conclusions reached are 

 here given. 



In both the Norway and albino rats the suprarenal glands of 

 the males are considerably smaller than those of the females. 

 When, however, these two forms of rats are compared, both sexes 

 of the Norway rats have suprarenals considerably heavier than 

 those of the like sexes of the Albino. 



A sex difference is noted in the weight of the hypophysis in both 

 the Norway and albino rats. The male hypophysis is lighter 

 than that of the female. However, when these two forms of 

 rats are compared, the hypophysis of the Norway is found to be 

 smaller than that of the albino rat; the greater difference being 

 in the case of the female. 



Neither in the Norway nor the albino rat is a sex difference 

 found in the weight of the thyroid. Moreover, there is no weight 

 difference in the thyroid according to variety in the case of these 

 two forms of rats. 



The sex glands (testes and ovaries) of the Norway rats are 

 heavier than those of the albino rats. 



Hatai is also of the opinion that the differences noted are again 

 the result of a response to domestication. 



4. Similarity of the Norway s and Albinos of western Europe to 

 those of the United States. It is to be noted in this connection 

 that so far as tests have been made, the albino rats found in Europe 



