SEXUAL CHARACTERS OF SOME DOMESTIC BIRDS. 15 



of the feathers of this region being male-like, i. e., they lacked the 

 brownish margin characteristic of the female. 



On September 14 the first male characters, as indicated by the mark- 

 ings and color of the plumage, had begun to appear. Later in the 

 year, when the juvenile to adult molt was completed, the bird had 

 essentially the same appearance as that given in the plate. Since that 

 time there has been no change in the character of the bird, though she 

 has molted several times. 



The bird, however, is not entirely a replica of a male. If the 

 mandible be compared with that of the drake in plate i it will be 

 observed that they are quite unlike. That of the male is typical 

 for his sex, while that of No. 169 is typical for the castrated female 

 and resembles that of the female. It differs from that of the nor- 

 mal female, plate 11, in having the dark-greenish patches, mostly 

 marginal, replaced by a clean yellow, or, to put the matter a little 

 differently, the black area of the normal female was not affected by 

 castration, but the dull greenish-yellow pigment did not develop. An 

 explanation of this failure possibly lies in the age at which the black 

 pigment becomes fixed. When first hatched, Rouen ducklings and 

 many hybrids have bills that are almost black. In ducklings a month 

 old the sexual differentiation of the mandible color toward that of the 

 adult has already begun. In the male the colors gradually lighten until 

 they reach the adult condition. In the normal females, however, very 

 little apparent change takes place in the region where the blotch of 

 the adult is located. The margins, however, gradually change to the 

 color of the adult. A further discussion concerning this change will 

 be found in a later section. It is possible, however, that something 

 very different actually occurs. It may be that the black pigmentation 

 of the mandible of the ducklings is a juvenile condition, and that in 

 each sex this disappears, leaving an underlying condition which it has 

 concealed. 



No. 182. The history of this individual contains several features of 

 particular interest. In the first place, the operation was performed 

 when the bird was 4 weeks of age. She is one of the youngest ducks 

 from which the ovary has been entirely removed. Hatched October 1, 

 of non-pedigreed ancestry, the operation was performed October 31. 

 Later developments show that the duck was of the " plain head" type 

 described in an earlier paper. The juvenile coat (i. e., first coat of 

 definitive feathers) was not distinguishable from that of the normal 

 female. Owing, perhaps, to the unfavorable conditions under which 

 it was necessary to keep the duckling during her first winter, she grew 

 very slowly and did not attain the adult plumage that winter. In 

 March she again came under the immediate care of the writer and was 

 given special attention. The more favorable conditions following on 

 the long period of adverse environment apparently induced a molt, for 



