88 HELEN DEAN KING AND HENRY H. DONALDSON 



A word of explanation touching the standard albino record 

 is necessary. The values are from reference table 148. This 

 table was made some fifteen years ago, when the Albinos used 

 for it were living under less favorable conditions than those 

 at present obtaining in our colony. One result of the im- 

 proved treatment has been to diminish the weight of the thy- 

 roid in the Albino, so that to-day, at the body length of the 

 captive Grays, the observed values for albino thyroid are 



52 per cent below the reference-table values for the males and 



53 per cent below for the females. 



Inspection of chart 19 shows a progressive diminution in 

 the weight of the thyroid with some fluctuations. In general, 

 the graphs for the two sexes run the same course, but the 

 average percentage deviation for the females is about 1 per 

 cent more than that for the males. This relation, according 

 to sex, calls for a word of comment. On body length the 

 weights for the female thyroids of the standard Albino sur- 

 pass those for the males by about 7 per cent, while in the wild 

 strain this sex difference does not appear. 



Since the basal values for the female Albino are 7 per cent 

 higher than for the male and since the thyroid weight in the 

 captive Grays is only 1 per cent below that of the males when 

 thus charted, it follows that in the captive Grays the thyroid 

 on body length is heavier in the females than in the males. 

 There is thus a shift toward the sex relations found in the 

 Albino. 



When compared with the data in table 204 (reduced to the 

 body-length basis), it appears that the wild gray Norways 

 have thyroid weights close to those for the Albino. From 

 this it follows that the deviation in weight shown by GI of 

 the captive Grays probably represents a marked loss in thy- 

 roid weight from that for the wild ancestors. It is evident 

 that in the case of the thyroid there is a progressive loss in 

 weight, in both sexes, from GI to G 10 . This has occurred dur- 

 ing the period of captivity and might be regarded as an effect 

 of captivity were it not for the behavior of the thyroid in 

 the Albino. In 1912, this albino strain, after many years in 



