INHERITANCE OF MINOR VARIATIONS IN INTENSITY. 



89 



In tables 39 and 40 are given the mean grades at birth and when 

 more than 4 months old for all guinea-pigs which were graded these two 

 times. These data are arranged by constitution and stock. In most 

 cases the mean grade at birth of the sample graded twice agrees well 

 with the mean grade at birth of the whole array of the same constitu- 

 tion and stock. 



Black Sep, 



Sep 



Fig. 6. — Variations in intensity of dilute blacks. Formula and stock 

 printed near mode of each distribution. 



VARIATIONS OF YELLOW. 



I owe the suggestion that heterozygous albinism may be correlated 

 with extreme dilution of yellow to Professor Castle, who found that 

 attempts to select for a cream stock of maximum dilution led to stocks 

 which invariably gave numerous albinos. The tables and figures con- 

 firm this suggestion in a very striking way. Animals known to be 

 homozygous dilute (C d C d ) vary between yellow 2 and yellow 4 with the 

 mean at yellow 2 . 9 . Those known to transmit albinism vary between 



