SEXUAL CHARACTERS OF SOME DOMESTIC BIRDS. 41 



EFFECT ON COLOR OF THE MANDIBLE. 



The effect of castration on the color of the upper mandible does not 

 correspond to that observed for plumage-color. No change has been 

 noted in fowl and none is to be expected, since the color of the mandibles 

 is the same in each sex of Leghorns. In Rouens the upper mandible 

 of the male, both normal and castrated, is uniform greenish yellow, in 

 the normal female dark greenish with a large central black area. In 

 the cross-bred birds the mandibles may be yellow in each sex. In 

 Gray Calls (Mallard in plumage color) the mandible of the male is 

 greenish yellow with a blotch like that of the female. In the castrated 

 female the central blotch remains, but the dark greenish color of the 

 margin disappears, leaving these parts yellow. Castration, then, is with- 

 out influence on the male's mandible color, but removal of the ovaries 

 results in the disappearance of certain pigments from the mandible of 

 the female, regardless of the age at which the operation is performed. 



The newly hatched ducklings are alike in the color of the mandible, 

 which is almost black. During ontogeny that of the male lightens up 

 uniformly until the adult color is reached ; that of the female, however, 

 lightens in certain regions only, corresponding to the pattern described. 

 In one lot of ducklings a month old the differences hi mandible color 

 were already apparent. Probably it will be necessary in operating to 

 anticipate such changes if a modification of the mandible color is to be 

 secured, but thus far attempts to ovariotomize ducklings a week or two 

 of age have failed. We are unable, consequently, to deternime the 

 exact relationship between the ovary and the blotch in the female's 

 mandible. It is hazardous to assume, from Analogy with other char- 

 acters, that the female mandible color is really dependent on the ovary, 

 but that its pigments have been deposited in an unchangeable state, com- 

 parable with that in a fully formed feather. Instead it is possible that 

 it is a unit character inherited according to some definite but unknown 

 scheme. In Gray Call ducks, as pointed out, the male has the central 

 blotch as well as the female. The male Rouen, exceptionally, may 

 have the ridge of the mandible darker than the rest. Since the " Stand- 

 ard of Perfection" calls for the mandible color described above, it 

 becomes more probable that the blotch represents a separate unit 

 character. 



EFFECT ON SIZE. 



It has long been known that the male mammal and bird, when cas- 

 trated young enough, grow larger than intact individuals. This is due in 

 part to the continued growth of the epiphyses of the long bones, though 

 at the same time there is a general increase in size. The present set 

 of experiments has not been of sufficient extent, nor has the stock been 

 sufficiently homogeneous in respect to weight, to give average results 

 of any value whatsoever. That is, the variation among normals is so 

 great that a comparison with the few castrated individuals might be 



