ON THE CHANGE OF COLOUR IN BIRDS. 87 
In order to illustrate the very different forms of the radii in 
various birds, and more especially the very different structure 
of the feathers in the winter and summer plumage of some birds 
which undergo a double moult, I give here, in addition, some 
drawings of the feathers of foreign birds, which I think will 
sufficiently refute the views of Schlegel and others on the change 
of feathers without moulting, or the possibility of one form 
growing out of another. 
Prats II., fig. 8, represents two branches of a breast-feather 
of the beautiful Nectarinia senegalensis, a male, in nuptial plumage. 
The red tips have ab initio no radii, nor are the blue radii lower 
down cast. These latter differ materially from, for instance, the 
radii of Linota linaria (fig. 4), inasmuch as they are fastened, 
not on the sides, but on the top of the branches. This may be 
clearly observed in fig. 9, a branch seen from the under side. 
The form of the winter plumage probably agrees with fig. 10, 
which is a portion of a breast-feather of Nectarinia formosa, a 
male, in winter plumage. Fig. 11 is a portion of a similar feather 
in nuptial plumage, taken from the same specimen in a state of 
transition to this plumage. 
Fig. 12 is a portion of a breast-feather from the middle of 
the breast of a male Ploceus rubritorquis in winter plumage. 
Fig. 13 is an orange-red branch from the nuptial plumage of 
the same species, and from the same locality. This bird, as 
also Ploceus longicauda, axillaris, albonotatus, capensis, and 
others, in addition to all the small feathers, changes the tail- 
quills twice a year. 
Fig.-14 is a portion of a green head-feather from Anas 
boschas, in the spring. After the autumn moult the square- 
pointed radii are furnished with small colourless points, which, 
however, soon fall off. The structure of the head-feathers of 
Anas clypeata bear much resemblance to this species, but the 
colour of the branches is not brownish, but white. Fig. 15 is a 
branch of a feather from the summer plumage of the same species, 
and from the same locality. 
The radii of the species represented in figs. 8 to 15 undergo 
naturally, also, a natural abrasion or wearing away; but this 
does not occasion a brighter tint of colour, being in reality a 
decay. 
