SEXUAL CHARACTERS OF SOME DOMESTIC BIRDS. 33 



several millimeters, together with the center and most of the base, but 

 along the edges of the tip, for about 6 mm., the feathers were dis- 

 tinctly male, the barbules being absent and the barbs orange in color. 



Like results have been obtained in several instances with the ducks, 

 but in only one is the interpretation free from complications, due to 

 the close resemblance of the female's plumage with both the juvenile 

 and summer plumages of the male and partly to the type of plumage 

 found in the females of Type II. There is no question, of course, as to 

 the nature of the male portion of the feather, provided it belongs to the 

 breeding plumage. Whatever questions may arise are in regard to the 

 female portion. Plate vi, p, shows one of these feathers. Doubtless 

 more instances would have come under observation if particular pains 

 had been taken to select birds in the right stage of development when 

 operated on. 



Feathers that even for a small portion are male along the margin but 

 female in the center, or vice versa, do not fit well with the suggestion 

 that the ovarian secretion does not persist long in the circulation. 

 However, another sort of explanation may perhaps be offered for such 

 cases, and that is that some of these characters are more responsive to 

 slight amounts of the ovarian secretion than others. From the evi- 

 dence presented above, it is quite certain that, although a minute 

 particle of the ovary may be present, the amount of secretion produced 

 may be insufficient to bring about the development of the female 

 characters. As this particle grows the amount of secretion produced 

 must constantly increase until it reaches a point where the male char- 

 acters are completely suppressed. In between these may be a region 

 where the amount of secretion present in the blood is sufficient to 

 suppress some male characters, but not all. 



A different explanation may be offered to account for those instances 

 where the color distribution in a transverse line is both male and female, 

 but where this condition covers a very small portion of the feather and 

 then gives way to a purely male or female condition, as the case may be, 

 since obviously the relation of the barbs to the axis while in the sheath 

 is sufficient to account for the final relationship of the characters. 



The whole matter is further complicated by considerable variation 

 in the characters in question, in some portions of the plumage at least. 



It may be possible to utilize this sort of data in studying the order 

 in which the various parts of the feather are laid down. Thus, those 

 feathers that have the margin on any transverse line of one color and 

 the center of another color indicate that the corresponding parts in the 

 feather germ are differentiated at different times, the margin being 

 formed later than the center. On the other hand, from those feathers 

 in which the transverse boundary line between the two colors is very 

 sharp, one could conclude that the differentiation extends in a well- 

 defined line transversely to the main axis of the feather cylinder. 



