100 HELEN DEAN KING AND HENKY H. DONALDSON 



Attention is called to the -fact that the data here to be -con- 

 sidered are from the first ten generations only of gray; Nor- 

 way rats in captivity. To obtain the full effects of captivity 

 on the body and its organs will probably require many more 

 generations, and, therefore, any conclusions drawn from the 

 present data must be largely tentative. 



Body size. This is best measured by body length, and 

 chart 12 gives the graph for the observed values. As the 

 entries in tables 11 and 12 show, the body length at GI is for 

 rats much over 600 days of age and at G 2 for those under 

 this age, while the remaining eight entries run close to 600 

 days. Correction for age would bring down the body length 

 at GI and slightly raise it at G 2 . Both changes are small, 

 however. 



If the graphs for body length are viewed with these pos- 

 sible corrections in mind, it is seen that the values for the 

 first three generations are low, but, in both sexes, giving 

 average values not essentially different from those for the 

 last three generations. Moreover, the unfavorable conditions 

 which were acting from G 5 to G 8 do not produce any clear- 

 cut effects as indicated by these graphs. The mean body- 

 length value for the series is 240 mm. for the males and, for 

 the females, 223 mm. Captivity has, therefore, not altered 

 the body length on age. 



Body weight. In chart 13 the relations of the body weights 

 as observed to those to be expected on the observed body 

 length (reference table 187} are shown by the graphs.' The 

 graphs also show that the observed values exceed the tabular 

 values for the wild gray Norways and that the excess tends 

 to increase in the successive generations, so that at GI O the 

 body weights of the captive Grays are in excess by 16.6 per 

 cent in the males and by 16.2 per cent in the females. This 

 excess in body weight is similar to that shown by the Albinos, 

 so that captivity for ten generations has developed in the 

 captive Grays the weight-length relations which are char- 

 acteristic for the Albino. However, the graphs sag slightly 



