306 



THE AMEBIC Ay NATURALIST 



[Vol. LV 



there is no evidence that any of the factors here under 

 observation are sex-linked and there is considerable evi- 

 dence that they are not, this omission is not serious. 



The results of these crosses are understandable on the 

 "assumption suggested in the earlier paper that the indi- 

 viduals from the recessive white races are homozygous 

 for the factors E and p, p being the recessive allelo- 

 morph of P, a factor necessary for the production of 

 black pigment in the feathers. Sturtevant (1912) first 

 suggested that Wyandotte white is recessive, a fact which 

 was overlooked in my earlier paper. Morgan and Good- 

 ale (1912, p. 115) have made a similar assumption for the 

 wliite Plymouth Kock. 



Since in the series of experiments being reported here, 

 reciprocal crosses of white Wyandottes and wliite 

 Plymouth Rocks gave only whites, thereby showing no 



