116 ANNALS NEW YORK ACADEMY OF SCIENCES 



presence or absence of barring, unless otherwise stated, was made on 

 newly hatched chicks, or those of full term which failed to hatch. This 

 method of determination is made possible by the presence of a gray 

 occipital spot on those chicks which will become barred adults. A full 

 discussion of the point, however, will be given elsewhere. Inroads of 

 vermin, largely rats, have limited the number of which the sex was de- 

 termined. A description of the adult hybrids is deferred until after all 

 the matings have been described. 



Explanation of the Symbols used in Interpreting the Results. — It was 

 pointed out by Spillman, following Bateson, that sex-linked inheritance 

 in poultry could be accounted for on the assumption that the female is 

 heterozygous for sex and the male homozygous, and that when in the 

 female, the barred factor alone is present, it is repulsed by femaleness. 

 We ma}^ give this interpretation a more concrete form, if we assume that 

 the factor in question is not carried by the same chromosome that carries 

 the factor for the female sex; i. e., in the heteroz}^gous female the chro- 

 mosone that carries femaleness also lacks the factor for barring, and its 

 mate that lacks the factor for femaleness carries the factor for barring. 

 No interchange between the chromosomes (if two really exist) can take 

 place, perhaps because they fail to pass through those stages in synezesis 

 when such a process becomes possible. 



If F = female, f its absence or male ; B = barred, b its absence ; N = 

 black, then the formulas for the barred fowls will be : 



Barred 9 FNb fNB 



$ fNB fNB 



For the Langshan fowls, the formulas will be : 



Black 2 FNb fNb 



$ fNb fNb 



Whether the female-producing gamete of the Barred Eock really car- 

 ries black or only the absence of barring will not affect the nominal 

 results here recorded, but other experiments to be described by Goodale 

 will show that "black" is probably present. 



In order to see how these formulas apply to the crosses under con- 

 sideration, let us take first the case of the cross between the Langshan 

 hen and the Plymouth Eock cock (fig. 1). The formulae are as follows: 



Langshan $ FNb fNb 



Barred Rock $ fNB fNB 



Barred 5 FNb fNB 



Fl "4 " $ ... fNb fNB 



