I obtained a series of specimens, illustrating the manner in which the extraordinary black tail ribands are developed, which is very remarkable.

They first appear as two ordinary feathers, rather shorter than the rest of the tail; the second stage would no doubt be that shown in a specimen of Paradisea apoda, in which the feathers are moderately lengthened, and with the web narrowed in the middle; the third stage is shown by a specimen which has part of the midrib bare, and terminated by a spatulate web; in another the bare midrib is a little dilated and semi-cylindrical, and the terminal web very small; in a fifth, the perfect black horny riband is formed, but it bears at its extremity a brown spatulate web, while in another a portion of the black riband itself bears, for a portion of its length, a narrow brown web.

It is only after these changes are fully completed that the red side plumes begin to appear.
The successive stages of development of the colours and plumage of the Birds of Paradise are very interesting, from the striking manner in which they accord with the theory of their having been produced by the simple action of variation, and the cumulative power of selection by the females, of those male birds which were more than usually ornamental.
Variations of _colour_ are of all others the most frequent and the most striking, and are most easily modified and accumulated by man's selection of them.

We should expect, therefore, that the sexual differences of _colour_ would be those most early accumulated and fixed, and would therefore appear soonest in the young birds; and this is exactly what occurs in the Paradise Birds.

Of all variations in the _form_ of birds' feathers, none are so frequent as those in the head and tail.