FIG. 3. One of the two F₁ castrated birds. For comparison see the colored drawing in plate 2, figure 4. FIG. 4. A castrated Sebright. This bird is darker, and in this sense more typical than figure 2. FIG. 5. One of the castrated Sebright males which at one time after castration was as extremely cock-feathered as figure 2, but slowly “went back” towards hen-feathering, as the figure shows especially in the hackle and saddle. The details are much better shown in the feathers photographed in plate 8, figures 1, 2, 3, 4, 1_a_, 2_a_, 3_a_, 4_a_, 1_b_, 2_b_, 3_b_, 4_b_. FIG. 6. The same bird was opened and the regenerated pieces of the testis removed. He returned later, as shown here, to full cock-feathering. PLATE 6. FIGS. 1, 1A. Typical old (1) and new (1_a_) feathers (after castration) of the same bird. This is the “lighter” male drawn in plate 1, figure 4, and photographed in plate 5, figure 2. FIGS. 2, 2A. Typical old (2) and new (2_a_) (after castration) feathers of another Sebright. This bird developed after castration darker feathers than did the last bird. Its feathers were more like those that other castrated Sebrights developed. Legend on plate 6 erroneous as far as 2 and 2a are concerned. PLATE 7. FIGS. 1, 1A. Typical old (1) and new (1_a_) (after castration) feathers of an F₁ bird. (See plate 2, figures 1 and 4.) FIGS. 2, 2A. Typical old (2) and new (2A) (after castration) feathers of bird shown in plate 3, figures 2 and 3 (No. 292). PLATE 8. Typical feathers of “dark” Sebright (1, 2, 3, 4) that after incomplete castration changed to cock-feathering (1_a_, 2_a_, 3_a_, 4_a_), then later, as pieces of the testes that had been left behind in the old situs regenerated, began to go back towards hen-feathering (1_b_, 2_b_, 3_b_, 4_b_). The bird was then opened again, and the regenerated pieces removed, when it again became cock-feathered (1_c_, 2_c_, 3_c_, 4_c_), and has so remained for more than a year. PLATE 9. FIGS. 1, 1A. Typical feathers of hackle and saddle from hen-feathered bird (No. 68) plate 3, figure 2, that changed over to the cock-feathered bird of plate 3, figure 3. FIGS. 2, 2A. Typical feathers of an F₁ male (2) that changed over partly as a result of degeneration of his testes, into a cock-feathered bird (2A). The change was not so great as it is after castration. FIGS. 3, 3A. Typical feathers of Sebright male that slightly changed towards cock-feathering (old hackle feather missing). PLATE 10. FIGS. 1, 1A. Old (1) and new (1A) wing-coverts of normal Sebright (1) and castrated (1A).