mechanical necessity, is commonly observed in chemical 

 experiments ? 



Obviously, the mass of the determiner for pigmenta- 

 tion is as potent a factor in determining the end result as 

 the mass of the destroying antibody. The kind or quality 

 of the pigment seems also to be a factor; the yellow or 

 sorrel pigments seem to be destroyed more readily than 

 the black or brown. It is also apparent that, due to a 

 difference in the relative mass of the determiner and the 

 antibody in the zygote, one cross may affect total destruc- 

 tion of the pigment while another parallel or reciprocal 

 one may not. Thus, as above mentioned, Davenport's 

 white Leghorn on black Minorca cross gave only white 

 or nearly white offspring, while his parallel cross, viz., 

 white Leghorn on black Cochin, gave considerable black 

 pigment in the offspring. It has also been observed that 

 the barred Plymouth Rock male, which is much less 

 heavily pigmented than the female, when mated with a 

 white Leghorn female gives only white offspring, but 

 the reciprocal cross, viz., the white Leghorn male on the 

 barred Plymouth Rock female gives barred, mottled, 

 gray, creamy and white offspring regardless of sex. In 

 this latter mating the two gametic elements, viz., the de- 

 terminer for pigmentation and the destroying antibody, 

 seem to be present in quite closely chemically balanced 

 masses and it would be interesting to know whether in 

 this cross the fluctuations across the color line are due to 

 accidental variations in the strength of the individual 

 gametic elements in question or to the Mendelian phe- 

 nomenon. 



some arctic animals such as the arctic fox. which is white 

 the vear around, and the arctic hare and the ptarmigan, 

 which are pigmented at one season and white at the 

 other. It would be interesting to know whether the fur 

 and feathers of these animals in their unpigmented 



