COLOR 47 



property transferable from one pigment (as black) to another (as yellow), 

 it is evidently due either to some modification in C, or else to an indepen- 

 dent factor. But it can not be due to C, since it is transmissible through 

 an albino, which by hypothesis lacks C. We are forced to conclude that 

 it is transmitted through some independent factor, which we shall desig- 

 nate I, intensity; it is alternative with D, a state of dilution (as in the blue 

 modification of black, or the cream modification of yellow). 



THE FACTOR FOR A PIGMENT PATTERN OF THE INDIVIDUAL HAIR, A. 



Evidence for the existence of a factor (A) governing the pigment pat- 

 tern of the individual hair has been presented elsewhere (Castle, 1070). 

 It was first recognized in the case of the guinea-pig (Castle, :o6) as an 

 essential factor of the " agouti " coat, indeed as the only feature which 

 differentiates the agouti variety from black. Hence the symbol A (agouti) 

 was adopted to designate it. Cuenot (104) employed the symbol G to 

 designate in mice the agouti or gray coat, and designated black by a differ- 

 ent symbol, but he failed to recognize that gray is simply black plus a 

 second factor. Hence his G equals B (black) plus A. Hurst has inde- 

 pendently discovered the existence of the A factor in rabbits (Proceedings 

 Seventh International Zoological Congress, unpublished). In the guinea- 

 pig, a new color variety, cinnamon-agouti, has been deliberately produced 

 through the agency of the independent factor A. (See Castle, : 08.) 



THE FACTOR FOR UNIFORMITY OF PIGMENTATION, U, OR SPOTTING WITH WHITE, S. 



The factor U (uniformity of pigmentation) is alternative with spotting 

 with white, S. Its existence was first established by Cuenot (104). Like 

 I, the intensity factor, it may be regarded as a modifier of C, though not 

 identical with it; for U and S are transmissible through albinos, which 

 themselves have no pigmentation and which by hypothesis lack the fac- 

 tor C. U is also demonstrably independent of any particular color, for 

 spotting with white is transferable in crosses from one color variety to 

 another, as, for example, from black to yellow. 



THE FACTOR FOR EXTENDED DISTRIBUTION OF BLACK OR BROWN, E, ALTERNATIVE 

 WITH R (RESTRICTED DISTRIBUTION). 



The assumed factor E is a modifier of black and brown, but not of 

 yellow pigmentation. It is alternative to R, a restricted distribution of black 

 and of brown pigments, in which distribution they are confined to the eyes 

 and to the skin of the extremities. The distribution of yellow pigment 

 (Y) is wholly unaffected by this factor. When black and brown are 

 restricted, yellow remains as the principal or even as the exclusive pig- 

 mentation of the hair (yellow varieties). 



That E really exists as an independent factor, and not as a condition 

 merely of black or of brown, is shown by the following experiment. If 

 one crosses a brown ("chocolate") guinea-pig with an ordinary yellow 



