II. SIZE OF THE BODY AND ORGAN > 81 



The captive Grays show, therefore, a slightly smaller brain 

 weight than the wild strain, but the terminal values at G,,, are, 

 if anything, a little above those at GI, so that there is no -\ i 

 dence of a progressive decrease in brain weight in the suc- 

 cessive generations. The low values at G 7 and G are con- 

 sidered as due to the unfavorable conditions in the colony 

 which acted on these generations during the early phases of 

 their development. It will not have escaped notice that tin- 

 weight of the brain in the original ancestors of the captive 

 Grays has not been considered. The data which we have indi- 

 cate a brain weight about that of the standard in the male 

 and some 3 per cent below the standard in the female, but 

 the number of cases is too small to give anything satisfactory 

 in the way of an average. The data suggest that there was 

 a sudden drop in the brain weight at GI. What this means, 

 if it occurs, is not at the moment clear. 



In view of the paucity of the data for the ancestors, the de- 

 viations which may occur between them and the GI generation 

 are not considered in the discussion that follows, and any 

 changes which are recorded are referred to GI as the starting 

 point. 



The slightness of the reduction in the brain weight of the 

 captive Grays was a surprise, as a much greater reduction 

 had been expected. This expectation was based on the fact 

 that when the data for the wild gray Norway (refer 

 table 187) are compared with the data for the Albino (refer- 

 ence table 144), using the body lengths found for the captive 

 Grays at G 10 , the wild gray Norway surpasses the Albino in 

 brain weight by 15 per cent in the males and 14 per cent in 

 the females. It is evident, therefore, that the reduction of 

 the brain weight of the captive Grays at GI O , which is 5 per- 

 cent or less in both sexes, marks only a slight shift toward 

 the relations characteristic for the Albino. To determine 

 whether the low brain weights characteristic of the Albinos 

 were shown by any individuals among the captive Grays, the 

 graphs in charts 15 and 16 have been prepared. The limiting 

 graphs give the extreme deviations plus and minus for each 



MEMOIR 14 



