6 THE GENETIC AND THE OPERATIVE EVIDENCE 



order to see if they would become cock-feathered. The outcome was 

 immediately apparent; the new feathers were those of the cock bird. 

 While the " reasoning" that led to the experiment is open to serious 

 question, nevertheless the "hint" furnished by the unusual condition 

 of the testis led finally to the discovery that luteal cells were present 

 in abundance in the testes of the male Sebright like those present only 

 in the females of other breeds. Whether or not the shape of the testis 

 of the Sebright, that is sometimes like that of the ovary, is connected 

 with the unusual abundance of luteal cells in the testis I do not know. 

 If so, then the hint that came from their shape was not so unreasonable 

 as appears at first sight. 



The birds first operated upon were adult Fi and F 2 hen-feathered 

 birds. The first one done by myself died, but a few, whose testes were 

 removed by Dr. H. D. Goodale at my request, lived and changed to 

 cock-feathered birds. Since then I have operated successfully on a 

 number of F x and F 2 birds, as well as Sebright males. In these opera- 

 tions I have had throughout the assistance of Dr. A. H. Sturtevant 

 and for two years the assistance of Dr. J. W. Gowen also. I wish to 

 express my appreciation of their help and advice, for without it I 

 doubt whether I could have carried out the work successfully. Since 

 the main interest attaches to the Sebright experiments, they will be 

 described first, although they were the last to be performed. 



CASTRATION OF SEBRIGHTS. 



Except for the similarities of the plumage, the male Sebright differs 

 as much from the female as do cocks of other races. The rose comb 

 is very large in the male, small in the female (plate 4, figs. 3, 4). The 

 wattles also are longer in the male. The cock carries himself erect, 

 as do the males of other breeds. His spurs are well developed and 

 he shows the aggressive behavior of his sex. On the other hand, the 

 shortness of the feathers on the back of the neck (the hackles), the 

 absence of the pointed feathers on the back and rump, and the usual 

 absence of long sickles and other tail-covert feathers make him 

 hen-like. The detailed account of the feathers in these critical regions 

 will be given when comparisons are made with the feathers of the 

 castrated birds (plates 6 and 8). 



Six males have been successfully operated upon and with one 

 apparent exception have all given the same results. The birds were of 

 somewhat different ages ; they had been hatched about July, and were 

 operated upon about November of the same year, when they were 

 either half grown or had nearly reached maturity. At the time of the 

 operation a few feathers were removed from different regions of the 

 body, and the new feathers that regenerated in the course of 3 or 4 

 weeks showed all the characteristics of those that came in later to 

 replace the juvenile or first adult coat. These regenerated feathers do 



