RELATING TO SECONDARY SEXUAL CHARACTERS. 95 



PART IV. 



SUMMARY AND CONCLUSIONS. 



1. The two principal results obtained were: (a) that castration of 

 hen-feathered Sebright males causes them to develop the full plumage 

 characteristic of the cock-bird ; (b) that complete hen-feathering is due 

 to two dominant Mendelian genes. 



2. A striking change takes place when the Sebright male is castrated 

 (plate 1, figs. 3, 4; plate 3, fig. 1). The new feathers on the upper 

 surface of the head, neck, back, wings, rump, and tail-coverts assume 

 a different color and distribution of their pigment ; they take on a new 

 shape, and in those regions where in the cock the barbules are absent 

 from a part of the margin of the feather, the same absence occurs in the 

 castrated birds. Such feathers are present on the neck, back, wing- 

 bow, and rump. The transition is shown in the figures in plate 6, 

 where for comparison one of the old and one of the new feathers lie 

 side by side. The tail-coverts in the hen-feathered bird are short, and 

 like those in the hen do not cover the true tail. After castration they 

 become excessively long longer, in fact, than in many cocks and 

 cover the true tail feathers. The tail feathers themselves, moreover, 

 become increased in length, as do the posterior row of feathers of the 

 wing-coverts. On the breast and sides the change is less marked. The 

 castrated Sebright loses his erect carriage, but how far this is due to the 

 changes in his plumage and how far is real (as a result of a new balance 

 due possibly to the lengthening tail and its coverts) I can not decide. 



3. While castration causes the hen-feathered male to make addi- 

 tions in color, length, and size of many feathers, it causes at the same 

 time the other retrogressive changes characteristic of the capon (a 

 castrated cock-feathered bird); the comb and wattles shrink and 

 become pale, the birds almost cease crowing, and become timid. They 

 do not make much effort to mate with the hens, but when they do they 

 show the usual copulatory reactions. 



4. If feathers are removed at the time of castration, the new feathers 

 show the full effect of the removal of the testes, although they must 

 have begun to develop immediately afterward. It is suggested that 

 by means of this delicate test the time relations of the internal secre- 

 tion can be profitably studied. 



5. Feathers that may have started their development at the time 

 of the operation show the old influence at the tip of the feathers 

 (plate 10) and the new one in the rest of the feather. The change is 

 abrupt, although the transition is perfect. 



6. Incomplete castration of the hen-feathered male leads to smaller 

 changes in the same direction than those following complete castration. 



Where such small pieces of the testis were left that complete cock- 

 feathering followed, the bird slowly changed back to hen-feathering 



