A hen-feathered male (No. 292) that was darker than the F₁ male--in fact, almost black, except for a yellow center in some of the dorsal feathers that were mossy or penciled--was castrated. The details of characteristic feathers may be gathered from the feathers in plate 7, figure 2. A corresponding set of the new feathers after castration, 2_a_, are paired with the former. The castrated male in his new plumage is shown in plate 2, figure 3. His dorsal surface is colored very much as is the same region in the F₁ bird, but the breast is very much darker, so that the bird as a whole presents a very different appearance from the F₁ castrated male. A very small white mass was found when the bird was killed in place of the old testis, composed, in sections, of a reticulated mass of cells that look like old broken-down follicles of testicular tubules with a few cell-layers lining the tubules. An F₂ male (68) also had dark feathers (plate 3, figure 2, and plate 9, figure 1). The castrated male in his new plumage is represented in plate 3, figure 3. Here again the upper surface is much like that of the last castrate, and also like that of the F₁ castrate. The breast has changed much less than the back; the centers of the feather are brown with a black margin and a black band at the tip. The exposed portion of the secondaries and the coverts are not so brown as in the last bird. The spurs of this bird were bent back, looking like the horns of a ram. When killed and examined, several small white pieces, that looked like pieces of testes, were found in the abdominal cavity near the old attachment of the testis. A histological study showed that these pieces contained tubular tissue apparently testicular, but without germ-cells. Another F₂ male (Band No. 221) was yellow in general color, the feathers being irregularly penciled. After castration (plate 3, figure 4) the bird became red above and deep brown below; the tail and coverts were black. A pale-yellow hen-feathered bird (No. 218) was also castrated. Here also the change was most conspicuous over the upper surface, not only in a greater depth of color than elsewhere, but in the shape, etc., of the feathers. On the breast the original yellow color remains, but is slightly deepened. When killed and opened (May 14, 1919), a few small, whitish pieces were found. When these were sectioned it was seen that they were made up, for the most part, of tubules looking like those of the epididymus and also a few testicular tubules. At the old situs there were some regenerated lumps, which in sections appeared to be loose glandular tissue. No germ-cells were present and the tissue just referred to may be old testicular tubules. HEWITT’S SEBRIGHT HEN THAT BECAME COCK-FEATHERED IN OLD AGE. Darwin records in Chapter XIII of Animals and Plants under Domestication a change that took place in an old female Sebright: