MENDEL'S law of inheritance rests on the assumption of random segregation of the factors for unit characters. The typical proportions for two or mzore characters, such as 9: 3: 3: 1, etc., that characterize Mendelian inheritance, depend on an assumption of this kind. In recent years a nunmber of cases have come to light in which when two or more characters are involved the propor-tions do not accord with Alendel's assumption of random segregation. The most notable cases of this sort are founid in sex-limited in-heritance in Abraxas and Drosophila, and in several breeds of poultry, in which a coupling between the factors for femaleness and one other factor must be assumed to take place, and in the case of peas where color and shape of pollen are involved. In additiorn to these cases Bateson annd his collaborat6rs (Punnett, DeVilmorin and Gregory) have recently published'a nlumber of new ones. In order to account for the res, ults Bateson assuames not only coupling, but also repulsions in the germ cells. Thefacts appearto be exactly comparable to those that I have dis-covered in Drosophila, and since these results have led me to a very simple interpretation, I venture to contrast Batesoni's lhypothesis with the one that I have to offer. The facts on which Bateson bases his inter-pretation may be briefly stated in his own words. namely:" that if A, a and B. b are two allelomorphic pairs subject to coupling and repulsion, the factors A and B will repel each otlher in the gametogenesis of the double heterozygote resultinjg from the union Ab X aB, but will be coupledl in the gametogenesis of the double heterozygote resulting from the union AB X ab," and further," We lhav-e as vet no probable surmise to ofTer as to the essential nature of this distinction, and all that can yet be said is that in these special cases the distribution of the characters in the heterozygote is affected by the distributioni in the original pure parents." Batesoni further points out that since" 4 sex in the fowls acts as' Proc. Royal Soc., Vol. 84, 1911 a repeller of at least three other factors,... some of them may be found able to take precedence of the others in such a way as to annul the present repulsion with subsequent coupling as a consequence." In place of attractions, repulsions and orders of precedence, and the elaborate systems of coupling, I venture to suggest a comparatively simple explanation based on results of inheritance of eye color, body color, wing mnutations and the sex factor for femaleness in Drosophila. If the materials that represent these factors are contained in the chromosomes, and if those factors that" couple" be near together in a linear series, then when the parental pairs (in the heterozygote) con1-jugate like regions will stand opposed. There is good evidence to support the view that during the strepsinema stage homologous chromosomes twist around each other, but when the chromosomes separate (split) the split is in a single plane, as maintained by Janssens. In consequence, the original materials will, for short distances, be more likely to fall on the sanme side of the split, while remoter regions will be as likely to fall on the same side as the last, as on the opposite side. In consequence, we find coupling in certain characters, and little or no evidence at all of coupling in other characters; the difference dependinig on the linear distance apart of the chromosomal materials that represent the factors. Such an explanation will account for all of the many phenlomena that I have observed and will explain equally, I think, the other cases so far described. The results are a simple mechanical result of the location of the materials in the chromosomes, anid of the methodI ofunion of …