132 ANNALS NEW YORK ACADEMY OF SCIENCES 



experimental evidence is flatly opposed to this latter interpretation, and, 

 therefore, until Guyer's evidence is confirmed or refuted, the case must 

 be left open. 



On the other hand, if, as the experimental evidence shows, barring is 

 "repulsed" by femaleness and if both of these factors are carried by 

 chromosomes, the formulas are deficient in having no chromosome to 

 carry barring, — a contradiction of terms. It may be, however, that the 

 X-chromosome in fowls has a mate which we may call Y which would 

 carry barring but not femaleness. The formulae would then be : 



Female X — Y 



Male Y — Y 



XY Female 

 YY Male. 



On this interpretation, the factor for femaleness would be contained 

 in X but absent from Y, while barring is contained in Y. This scheme 

 is compatible with the experimental evidence and gives consistent results 

 for all combinations. 



The irregularities that have been observed in the "reduction division" 

 both in birds and in man suggest the possibility that the sex chromo- 

 somes are united to other chromosomes as in some other animals. If the 

 union is variable, as in the nematodes, it may be that the X and the Y 

 (if Y exists) may sometimes pass to the poles of the spindle during 

 reduction in conjunction with other chromosomes and sometimes be free 

 to pass to the poles independently. If further study should establish 

 this view, it will have a very direct bearing «m the relations discussed 

 above. If the factor F for femaleness is carried by chromosomes attached 

 to one member of another pair, the mate of this member may be the 

 chromosome that carries the factor for barring. If this were the case, 

 however, interchange between these two members would lead to the 

 barring factor being transferred to the chromosome attached to the sex 

 chromosome. This is in contradiction to the experimental evidence 

 which would lead rather to the conclusion that a Y element lacking 

 the factor for barring is present. The Y may be attached to the mate 

 of the chromosome carrying the sex factor. 



At present, only a few cases have been discovered in which a sex-linked 

 character is dominant, viz. : in fowls and in one character in Drosophila. 

 The only other cases, besides the one in poultry in which sex-linked in- 

 heritance occurs and sex is heterozygous in the females, is that of Abraxas 

 and that of canaries. In both of the latter, the sex-linked factor is re- 



