38 The Bird 
as long and as perfect as the main feather. The origin 
and use of this feather-double is not known. 
Parrots, herons, and some other birds have a most 
convenient arrangement—a kind of automatic clothes- 
cleaner and valet combined. Concealed by the long body- 
plumage are several dense patches of down-feathers which 
grow quite rapildy, but instead of constantly increasing 
in length, the tips break up into a fine, white, greasy 
powder. This works its way through the entire plumage, 
and is doubtless of use in keeping the feathers in good 
condition and the body dry. Most of the birds possess- 
ing this convenience are comparatively free from lice, so 
this natural dressing may be as unpleasant to these ver- 
min as camphor-balls are to clothes-moths. 
The forms and textures of feathers are innumerable, 
and the uses to which they are put, more than we would 
ever imagine, but these will be spoken of under the chap- 
ters treating of the different parts of the body where they 
are found. 
Arrangement 
In examining a nestling we will notice that the feather- 
dots are not scattered at random over the surface of the 
skin, but grow in lines and tracts, whose limits are very 
sharply defined. In an adult bird, say an English Spar- 
row, this is even more noticeable. If we part the feathers 
on the centre of the breast, a broad, bare area is seen, 
with only a thin scattering of soft downy feathers. Under 
the wings are other naked spaces, and several more are 
on other parts of the body. The most ancient birds were 
