340 LIFE HISTORY 



'14). These plus characters of the Norway tend to disappear 

 when the Norway is subjected to domestication. 



The deviations of the wild Norway may be expressed in another 

 way. When the body weights of Norw^ay and Albino are the 

 same : 



The wild Norway rat has a greater body length; a greater brain 

 weight; a greater spinal cord weight; a higher percentage of water 

 in the central nervous system ; heavier ovaries, testes and supra- 

 renals, but a smaller hypophysis. 



When the body lengths are the same : 



The Norway rat has a smaller body weight; a greater brain 

 weight; a greater spinal cord weight; a higher percentage of water 

 in the central nervous system; heavier ovaries, testes and supra- 

 renals, but a smaller hypophysis. 



Speaking generally therefore, we may say that when compared 

 with the domesticated Albino, the wild Norway rat weighs more, 

 is longer and possesses a nervous system in which both the brain 

 and spinal cord are relatively larger. 



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), Lapicque and Girard ('07) and Donaldson ('23). 



There are still other observations w^hich 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 in both forms. The conclusions reached are 

 given in Chapter 14. 



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 

 Western Europe are similar to those found in America. For the 



