522 



THE AMERICAN NATURALIST 



[Vol. XLV 



Should it later prove possible to separate the two Watson 

 F 2 types, WWhh and Wwhh, as we can the corresponding 

 Holstein types, we should then have the interesting ratio 

 9:1:2:1:2:1. 



There is evidence in my material that the Holstein and 

 Small Eye types are still further influenced by one or 

 more additional factors. This matter is now under inves- 

 tigation. These additional factors appear to act in a 

 manner entirely similar to the factor H, but have less 

 effect. Taking the formula for Small Eye and adding a 

 factor I, similar in effect to H, we should have the three 

 types wwhhll, wwhhli, and wwhhii, all three of which 

 appear to be distinguishable, giving probably the three 

 types a, b and c of Fig. 1. This point will be studied in F 3 

 of the original crosses, of which a vast quantity of ma- 

 terial is growing, as well as in new crosses now being 

 made. 



In the above hypothesis the factors W and H were 

 assumed to have the property of enlarging the pigmented 

 area. The facts can also be explained by assuming that 

 w and h have the power of reducing the pigmented area. 

 In fully pigmented races, on this hypothesis, these factors 

 are absent. When w is introduced the pigmented area is 

 reduced to the Holstein pattern, h, without w, reduces 

 it to the Watson pattern, while w and h together produce 

 the Small Eye pattern. It is necessary in this case to 

 assume W and H dominant, respectively, to w and h, as 

 in the first hypothesis. 



We may also assume a factor W for Watson Eye, a 

 factor, E, allellomorphic to W, for Small Eye, and a 

 third factor, S, which tends to enlarge the pigmented 

 area, converting Small Eye into Holstein, and Watson 

 Eye into Solid Color. Here, W must be epistatic to E. 

 Under these assumptions the formula) of the principal 

 color patterns would be : 



Other Hypotheses 



EESS. 

 WWss. 

 EEss. 



