8 GONADECTOMY IN RELATION TO THE SECONDARY 



The plumage of the birds used in these experiments requires especial 

 attention, partly because of the marked difference in the sexes, partly 

 because of its complex nature and the succession of plumages during 

 the life of each individual. At least two sets of patterns influence the 

 general color of the bird. There is, first, the body pattern, which 

 depends upon the arrangement of feathers of different form and color 

 upon the body ; superimposed on this body pattern are the patterns of 

 the individual feathers. Any one follicle, however, may produce dif- 

 ferent kinds of feathers at different periods in the life of the bird. Thus 

 all normal individuals, both ducks and fowl, experience a succession of 

 plumage from the time they emerge from the egg to old age. What 

 constitutes the adult plumage is a little difficult to say, for in some 

 cases no plumage is quite like that which preceded it. In some varie- 

 ties the difference between the plumage of the first and second winters 

 is greater than that between the second and third. However, in both 

 ducks and fowls the strictly juvenile plumages are quite distinct from 

 the first mature plumage, so that for present purposes the plumage 

 worn during the first winter by spring-hatched birds may be considered 

 adult. In ducks there are three plumages: down, juvenile, and adult. 

 In Brown Leghorns there are four: down, chick, juvenile, and adult. 

 The distinctions between these plumages, as will be observed from the 

 appended descriptions, are for the most part sharp and clean-cut at 

 the height of development. Usually, however, because the plumage is 

 changed piecemeal, two succeeding stages are intermingled. The 

 descriptions are not intended to cover all details or all variations. 



ROUEN DUCKS. 



Down plumage. Sexes indistinguishable; feathers in the form of down. Body : dull black 

 dorsally; ventrally, yellow with a dark stripe through the eye and a similar one a little lower 

 on the cheek and four dull yellow spots on the dorsal side of the body (plate vn, fig. D) . 



Juvenile 1 plumage. Sexes similar but distinguishable; the down gives way to ordinary 

 feathers; head stripes persist but the spots disappear; contour feathers dull black, with 

 brown margins in the female. The male is similar, except that there are no brown margins 

 on the feathers of the rump and dorsal surface of the wing; the rump feathers are greenish 

 black; a few vermiculated feathers are present in various parts of the body. 



Adult plumage. Sexes quite unlike. Female (plate n): 2 head stripes persistent; entire 

 plumage dull black and brown, the feathers sometimes penciled (plate vi, o), sometimes 

 marked irregularly (plate vi, m,) ; no well-defined color areas. Male (plate i) : no head 

 stripes; several well-defined color areas, viz, green head, brownish purple breast, silver gray 

 ventral regions, greenish black rump; remainder of dorsal surface dull black. 3 



BROWN LEGHORN FOWL. 



Down plumage. Sexes indistinguishable; mid-dorsal region rich reddish-brown edged 

 with dark brown or black, becoming yellowish ventrally ; a dark-brown stripe passing through 

 the eye is separated from the top of the head by a buff stripe. Back with a longitudinal 

 stripe on each side of buff and brown. Sometimes the buff stripe is nearly white, sometimes 

 the brown is nearly black. 



lr The word "juvenile" is used here for all plumage phases of the young and not in the limited 

 sense used in the preceding section. 



2 In all the figures, due allowances must be made for the difficulties of reproducing the exact 

 color values of the original specimen. 



3 The speculum, i. e., iridescent blue bar of the wing, is alike in each sex. 



