144 THE STRUCTURE AND LIFE OF BIRDS cuap. 
Rhea—may be found primitive feathers that are not 
very different from the scales on the bird’s own legs 
or on a lizard. Birds in general have down feathers 
among the large ones, and these down feathers are 
often merely a little fluff at the top of a quill, though 
sometimes they are almost perfect miniatures of a 
typical feather.. Besides these there are thread- 
feathers, filoplumes, always growing close to the 
base of one of the large feathers. Sometimes, like 
hair, the thread-feathers are perfectly simple and un- 
branched ; the branches are never more than a very few. 
The Nightjar has, bordering the mouth, a number of 
bristles that look like filoplumes, but are really ordinary 
feathers of which only the shaft remains. There are also 
found on some birds, notably on some Parrots and on 
the Heron, powder-down feathers, so called because 
they shed a fine powder. They continue to grow, and 
the ends of their branches give off a whitish dust which 
is at once greasy and dry. What purpose they may 
serve is quite uncertain. 
By the help of these simpler specimens we must 
try to realise that the most elaborate feather is only 
a much-divided scale. Such a feather I must now 
describe, and then try to show how it has grown from 
a skin papilla. Take a large one from the wing or 
tail of any common bird. The semi-transparent base 
is the quill (Q, fig. 38); it has two small apertures, 
one at the bottom, the other at the top, where the 
branches begin, on the under-surface (U1 and 2). 
At the lower one the papilla entered to give the need- 
ful nourishment, and if a young feather be taken, the 
quill will be found full of blood (P). 
