PIGMENTATION OF THE VERTEBRATE SKIN 593 



Leghorn in the area of transplant, at least during the development of nestling 

 lown and juvenile feathers. Barred Rock melanophores produce barred feather 

 patterns in White Leghorn, New Hampshire Red, Black Minorca, etc. These 

 results demonstrate that the introduced melanophore produces the color pat- 

 tern in the feather in the immediate area of the implant. 



Various genetic studies (see Dushane, '44, for references) have demon- 

 strated that the Barred Rock factor is dominant, and that it is sex-linked. For 

 example, if a Barred Rock hen is crossed with a Rhode Island Red cock, the 

 Fi male will contain two sex chromosomes, one from each parent. That 

 :hromosome from the female parent will have a Barred Rock factor, whereas 

 that from the male parent will not. The Fi cock, therefore, is heterozygous 

 for barring, and, as the barring factor is dominant, the Fi cock will show 

 barred feathers. The Fi female, however, derives its single sex chromosome 

 from the male parent; as this chromosome does not contain the barring factor, 

 the Fi female is black. 



Willier ('41) presents evidence concerning the transplantation of melano- 

 phores from Fi heterozygous males and Fi heterozygous females of this Barred 

 Rock cross. Transplanted melanophores from an Fi male into White Leghorn 

 hosts always produce barred contour feathers in either sex, whereas Fi female 

 melanophores transplanted to White Leghorn hosts always produce non-barred 

 or black regions. Danforth ('29) demonstrated that the barring factor in the 

 skin of the male donor at hatching, when transplanted to a female host at 

 hatching which lacked the barring factor, produces barred feathers in the 

 female host in the area of the transplant. The results obtained by Danforth 

 suggest that the barring gene acts independently of the sex hormone, although 

 the feather type present in the graft assumes the female characters of the 

 host and, hence, is affected by the female sex hormone. The results of these 

 experiments by Willier and Danforth suggest that the barring gene in poultry 

 acts directly upon the melanophore and not upon the environment in which the 

 melanophore functions. (For extensive description, references, and discussion 

 of these phenomena, consult Danforth, '29; Willier, '41; and Dushane, '44.) 



d. Examples of Hormonal Comrol of Chromatophoric Activity 



In the indigo bunting, the male resembles the female during the non-breeding 

 season. During the breeding season, however, the male develops a brilliant, 

 purple-colored, highly iridescent plumage. Castration experiments and gonado- 

 trophic hormone administration suggest that this nuptial plumage is dependent, 

 not upon the male sex hormone, but upon gonadotrophic hormones elaborated 

 by the pituitary gland in the male. In the female, however, the presence of 

 the female sex hormone inhibits the effects of the pituitary gonadotrophins; 

 hence, she retains the sexually quiescent type of plumage (Domm, '39, p. 

 285). Also, in certain cases where the color of the bird's bill is a sex-dimorphic 

 character appearing during the breeding season only, it has been shown that 



