No. 600] PIEBALD RATS AND MULTIPLE FACTORS 721 



generalizations that have been made, and not directly on 

 the data. In this paper the writer has nsed the original 

 data, making verifications where possible, and recalcula- 

 tions of many of the constants. A few inconsistencies 

 and arithmetical errors were found. 



That there may be no misunderstanding as to the na- 

 ture of the multiple factor interpretation, the following 

 scheme is suggested. In the absence of any factor that 

 determines uniform color— in other words, in the pres- 

 ence of two doses of the factor for hoodedness— H;he 

 amount of pigment on hooded rats may be influenced by 

 several factors. Some of these increase, others reduce, 

 the pigmented area. The factors that increase the pig- 

 mented areas (plus factors) form Mendelian pairs (alle- 

 lomorphs) with the factors that decrease the pigmented 

 areas (minus factors). Dominance is lacking; if a factor 

 is contributed to the zygote by both parents, that factor 

 has more power than if it had come from only one parent. 

 Furthermore, environment, or other conditions which are 

 not inherited, being outside the germ plasm, have such a 

 modifying influence on the pigmented areas that the po- 

 tential differences between individuals determined by dif- 

 ferent combinations of factors in the germ plasm, are fre- 

 quently concealed. It is not pretended that this is the 

 only application of the multiple factor hypothesis that 

 can be made, but it is hoped that the following arguments 

 may become more significant with this suggested applica- 

 tion in mind. 



The writer herein undertakes to show that the concep- 

 tion of multiple factors may still be applied to Castle's 

 data. The points that favor the multiple factor interpre- 

 tation of the rat experiments, as well as certain objections 

 that are said to definitely disprove this theory, are brought 

 together in the following paragraphs. 



Points Favoring the Multiple Factor Interpretation 

 1. The gradual divergence of the plus and the minus 

 races may be brought about by the sorting out of groups 



