466 



THE AMERICAN NATURALIST 



[Vol. LVI 



buffs e"'e"'ss. Blacks are therefore genetically buffs with an 

 epistatic gene for the complete extension of black pigment. 



3. Extension of black is incompletely epistatic over silver so 

 that in fowls of the genotype E"'e"'Ss (male) or E"'e"'8-{ie- 

 male) silver appears in certain parts of the plumage, produ- 

 cing a pattern like that of the Dark Brahma. 



Collateral evidence indicates that the gene for extension of 

 black pigment (or one with similar effects) is present in Barred 

 Plymouth Rocks and White Plymouth Rocks (as a cryptomere) ; 

 and that it is absent in Columbian and buff varieties and in 

 Rhode Island Reds. 



Hurst^ was probably dealing with the same gene in his crosses 

 between Black Hamburgs and Buff Cochins, since Fj from this 

 cross consisted of all black chicks, while in F2 black and buff 

 chicks occurred in the proportions of 88 black: 31 buff. In in- 

 terpreting the results of this cross Morgan* states that either 

 one or two pairs of factors may be involved; which is right 

 "could only be determined by an ratio." Yet the F2 ratio 

 is given by Hurst (p. 138) and is surely a sufficiently close ap- 

 proach to a monohybrid ratio. The ratios obtained in our ex- 

 periments agree throughout with a mono-factorial interpreta- 

 tion. 



It is believed that this gene will be found to characterize 

 many color varieties of fowls in which black, either as a self 

 color or as a component of a pattern extends to all or nearly all 

 of the plumage. Concerning its origin no direct evidence can 

 be offered at prasent. Its occurrence as a discrete unit indicates, 

 however, that its origin was discontinuous and that black varie- 

 ties probably had their genesis in mutation rather than in selec- 

 tion of particolored types toward black. 



L. C. Dunn 



THE EFFECTS OF SO-CALLED CONJUGATION IN 



SHELLED RHIZOPODS^ 

 The phenomenon of conjugation in the Protozoa is regarded 

 as the forerunner of sexual reproduction in the higher animals, 



3 Hurst, C. C, 1905, Reports to the Evo. Comm., IT, pp. 138-39. 



4 Morgan, T. H., 1919, Publ. Carnegie Inst. No. 285, p. 24. 



1 The experimental work on this problem was carried on in the Zoological 

 Laboratory of the Johns Hopkins University. I wish to thank Dr. H. S. 



