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THE AMERICAN NATURALIST [Vol. XLII 



It is noteworthy that the male lacticolors produced in these 

 experiments were the first known, all known specimens of the 

 variety having been females. The reason for this is not far to 

 seek. Male L's occur only when female L's mate with hetero- 

 zygote males. The latter arise (from G parents) only in those 

 matings which produce female L's (see mating No. 4 above). 

 Heterozygote males are therefore as rare as female L's. If 1/n 

 of the female population is L, then 1/n of the male population is 

 heterozygote. The chance that these two shall mate is therefore 

 1/n X 1/n = 1/n 2 . Hence, if only 1 female in 1,000 is L, only 

 one male in 1,000,000 is L, which probably accounts for their 

 having escaped the collector. 



In the above case the female sex character seems to be paired 

 with G. This is indeed a highly interesting fact, if true, and 

 the results of Doncaster and Raynor leave little room for doubt 

 that it is true. It now seems probable that sex is a property of a 

 particular chromosome. 5 If this is the case, then the G character 

 should also belong to a particular chromosome. 



Bateson 5 also calls attention to what appears to be a similar 

 case of allelomorphism between the sex character and a color 

 element, in the case of black pigmentation of silky fowls, when 

 crossed with Brown Leghorns or other fowls with light shanks. 



I desire now to call attention to a similar case that has come 

 under my own observation. It is well known to breeders of 

 Barred Plymouth Eock fowls that an occasional black bird crops 

 out in this breed, and that these blacks are invariably females. 

 Mr. J. F. Spilman, of Wentworth, Mo., tells me that he once 

 crossed some Black Langshan males on his Barred Rock females 

 with the result that in the progeny all the females were black 

 and all the males barred. I have also seen, at the Mississippi Ex- 

 periment Station, some crosses between Barred Rocks and Indian 

 Games in which part of the progeny was black, the remainder 

 being barred. Unfortunately, in this case, no observations were 

 made as to a possible relation between color and sex. While the 

 data just given are insufficient to establish beyond question the 

 following explanation, the explanation is given in the hope that 

 it may stimulate investigation on this point. Let us suppose 

 that the female sex character (F) is paired with the barring 

 element (B). Let f == absence of F and b= absence of B. 

 Then a cross between a female Barred Rock and a male Black 



