HEREDITY 



show that the capacity to form pigment of all 

 sorts may be lost by a single variation, which 

 we have called loss of the color factor, C. We 

 do not know whether it consists in the loss of 

 a substance capable of oxidation, or of the 

 power to take some indispensable first step in 

 the process of oxidation, perhaps due to loss 

 of an enzyme; but we do know that when this 

 particular variation has occurred, the power 

 to produce other than albino individuals can- 

 not be recovered by any known means except 

 a cross with colored animals. We know also 

 that the capacity to form specific kinds of pig- 

 ment (yellow, brown, or black) is independent 

 of the general color-factor, C, for albinos may 

 transmit those specific powers without them- 

 selves being able to form any kind of pigment 

 at all, i. e. without possessing C. Any animal 

 which forms pigment of one of the higher 

 grades has the capacity apparently to form 

 pigment also of the lower grades. Thus a 

 black animal can form also brown and yellow 

 pigment granules. Brown (chocolate) animals, 

 however, lack the capacity to form black pig- 

 ment. The oxidation, it would seem, can in 



