During the spring of 1917 it was noticed that the bird was going back towards the hen-feathered type, and by the end of the summer he was in the intermediate condition, as shown by the photograph and by the individual feathers (plate 8, 1_b_, 2_b_, 3_b_, 4_b_). The comb had begun to enlarge also. The bird was opened again (1918) and pieces of testis about as big as peas were found on one side. Evidently a piece of the old testis had been left behind and had regenerated. As it enlarged the new feathers were affected so that the plumage returned towards the normal type. The pieces of testis were removed and a few feathers plucked out. The new feathers that came in were typically cock-feathered, and, as the molting proceeded during the winter and spring, the bird became cock-feathered for a second time as shown in photograph (plate 5, figure 6) and by the feathers in plate 8, 1_c_, 2_c_, 3_c_, 4_c_. Here, then, is an excellent example of the connection between the gonad and the condition of the plumage. On opening this bird (May 1919) no pieces of testes were found. There was a very small whitish lump at the situs of the old testes, which, when sectioned, showed some glandular-like tissue, not in tubules, and no evidence of testicular tissue. Three other younger Sebrights of the same stock were successfully castrated. They were hatched in June or July and castrated in November of the same year. They remained quite small birds, despite their elongation due to the long tail and tail coverts that they developed. One of these birds in his cock-feathered plumage is shown in plate 3, figure 1. One has died, the other two are alive and markedly cock-feathered, as shown in plate 6, figure 2_a_. All three birds were dark red-brown, much more so than the two preceding cases, especially the first case. This color difference might be attributed to the earlier age of the three birds when operated upon, or to a more complete (or less complete) operation involving perhaps neighboring parts, or to the birds having a somewhat different genetic composition (_i. e._, modifying factors). There is no special reason why the operation if performed early should have a different result on feathers that develop after the bird is of adult age. Goodale has suggested that there may be organs in the vicinity of the testis that have some influence on the kind of plumage produced, and if there are such organs they might be removed in one bird and accidentally left in another. It would not, however, be probable that the bird operated on at first had received one treatment and the later ones the other treatment. It seems to me more probable that the birds have come from different genetic strains, and that this genetic difference gives a more plausible explanation of the darker cock-feathered plumage. Goodale observed, for the first time I think, that the largest wing coverts of the castrated cock become longer. I looked, therefore, with some interest at the condition of