LIFE PROCESSES : SIZE OF BODIES AND ORGANS 7 



causes, such as unconscious selection applied to the albino 

 strain. As contributory to this end, the effects of captivity on 

 the wild gray Norway have been selected for study. 



It may be remarked that the term 'captivity' is here used 

 for the conditions under which the caged rats have been kept. 

 The term 'domestication' has previously been employed to 

 describe these same conditions, but as this latter term has 

 wider connotations, such as a modification of the animal to 

 meet human needs which is absent in this instance the 

 term 'captivity' has been preferred, implying, as it does, 

 merely a restricted range of activity and feeding, rather than 

 foraging. 



A general statement of the differences between the two 

 races is given in "The Rat" (Donaldson, ''24. p. 383). The 

 wild Norways are more excitable and much more savage. 

 They gnaw their cages. The body weight is less for a given 

 body length, hence it is a slighter animal. The skeleton is 

 relatively heavier, also the suprarenals (both sexes) and the 

 testes and ovaries. The thyroid is of like weight, but the 

 hypophysis distinctly lighter, in both sexes this last differ- 

 ence being most marked in the female. On the other hand, 

 the brain and the spinal cord are both heavier than in the 

 Albino. The special relations will be noted as they come 

 up for discussion. 



It should be kept in mind that the present report applies 

 only to the first ten generations of captive gray Norway-, 

 and is, therefore, a preliminary and tentative statement of 

 results, since these data do not afford a basis for final con 

 elusions. The observations are being continued and at pres- 

 ent the nineteenth generation of these captive Grays has been 

 obtained. 



The selection of the first ten generations for tn-atment a> 

 a group depends on the fact that in the eleventh generation 

 the strain 'broke' and several mutant varieties appeared, so 

 that these ten generations are marked off ly this event from 

 those that follow. 



