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THE AMERICAN NATURALIST [Vol. LII 



are like the blue-splashed in that homologous pigmented 

 feathers in both sexes have the same condition with ref- 

 erence to the restriction of pigment in the feather struc- 

 ture. 



2. The fundamental phenotypic differences between 

 black, blue and blue-splashed Andalusians are briefly 

 described. 



3. It is pointed out that the 1:2:1 ratio is in reality a 

 combination of two 3:1 ratios. 



4. The condition in the blues is shown to be due to the 

 combined action of two factors R and E. R acts on black 

 pigment, restricting its distribution in such a way that it 

 gives the characteristic blue-gray appearance. E extends 

 black pigment to every feather on the fowl's body. 



5. It is impossible to decide on the basis of present 

 facts whether R and E are located on identical loci of 

 homologous chromosomes or are the dominants of two 

 pairs of factors, each linked to the recessive allelomorph 

 of the other. 



6. It is shown that if the latter is the condition, crossing- 

 over might occasionally occur between R and E with small 

 likelihood of detection. 2 If crossing-over does occur, RE 

 gametes are possible, which appears in turn to make pos- 

 sible true-breeding blues. 



Acknowledgments 

 It is a pleasure to acknowledge my indebtedness to Dr. 

 Leon J. Cole and Professor Jas. G. Halpin, of the Uni- 

 versity of Wisconsin. The blue Andalusian problem was 

 undertaken at Dr. Cole's suggestion and the work is 

 being continued under his direction. I have consulted 

 him freely during the preparation of this paper. Pro- 



matings," that is, one male is mated to a number of females and the off- 

 spring from these females are not kept separate. The exact parentage of 

 any individual is therefore known only with regard to its sire, since its dam 



over depends upon the results of individual matings, it would be practically 



