The extent to which the change has taken place is best shown by comparison of individual feathers from identical regions—one before and one after the new feathers (taken out two years later) have come in ([plate 7]). The contrast between the old and new feathers of the hackle, saddle, back, and wing-bow are the most striking. In all of these the new feathers have become red on the exposed portion and the margin is free from barbules, as in the cock bird. The increase in size and change in shape of these feathers is remarkable. Equally great is the change in the tail-coverts that grade into those of the saddle at the base. The two median coverts or sickle feathers are longer than the tail and much arched. They are jet black with a purplish iridescence and with a yellow-red shaft. The tail itself has also changed; it has lost its stippling, and has become black like the coverts. The increase in length of the tail feathers is as remarkable as the increase in length of the coverts. A detailed account of these changes follows:
| F₁. | CASTRATE. | ||
| 1. | The head feathers are yellow with black base that shows through on the head. | 1. | The feathers are entirely red. |
| 2. | The hackle feathers are yellow with black base (showing through on neck). | 2. | The hackle feathers are entirely red. |
| 3. | The red feathers of the back are penciled. There is a black band, especially around tip just inside of the margin. | 3. | Feathers of back are red except for black at base. Barbules absent at end and side. Tip pointed. |
| 4. | The saddle feathers are much like those of the back, much stippled in center. The border is more distinct. | 4. | The saddle feathers are red with black base. They are long and pointed. |
| 5. | The tail coverts are similar to those of the hen. | 5. | The coverts are blue-black, with brown shaft. They are long, pointed, and curved. |
| 6. | The tail feathers are black, and with exception of the lower feathers they are partly stippled. | 6. | The tail feathers are black, not stippled, and have a black shaft. |
| 7. | The wing-bow feathers are penciled like those of the back. | 7. | The wing-bow feathers are red with black base. |
| 8. | Feathers on crop yellow with black spot at tip; those lower down on breast have a bigger spot. | 8. | Over the crop the feathers are orange-brown; on the breast they have the same color and a small black tip. |
The F₁ bird from which the colored drawing (plate 2) was made and from which the normal F₁ feathers were pulled was lent to Dr. Goodale in the summer of 1917. The bird died in April 1918, and his skin was sent to me. He also had begun to change over to cock-feathering ([plate 9], figures 2, 2a). Goodale recorded that the testis had dwindled to small bodies only about 10 by 5 mm. This accounts for the change to cock-feathering. For comparison I have added a third set of feathers to the two former sets, showing the new hackle, back, saddle, wing, and bow feathers of this bird. The feathers show that the change is in the same direction as that shown by the castrated cock, but it has not gone so far in the direction of cock-feathering. The tail is still short and the feathers are black. The sickle feathers are not longer than the tail and are stippled. It is probable that this is the old tail whose feathers have not been molted since the testis dwindled. In fact, elsewhere the old and the new feathers are both present, showing that a complete molt had not taken place. The old feathers still present are practically like those of the original F₁ bird, showing that the change was of recent date, and due to the decrease in the testis which was probably caused by disease.
CASTRATION OF F₂ HEN-FEATHERED MALES.
The F₂ hen-feathered males from this cross could not be utilized until they had begun to assume the adult plumage, since before that time they were like the cock-feathered F₂ males. Consequently, the operation is more difficult and more dangerous to the bird. A good many birds have died in consequence of the operation, but enough successful operations (five) were made to show what the color of certain types of hen-feathered bird would be when changed to cock-feathering.
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, 2a, 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.