264 
COLOUR IN NATURE 
CHAP. 
Each barb bears two rows of barbules, and one of these 
rows points to the tip of the feather, and the other 
to its outer or inner edge. The latter is called the 
proximal, and the former the distal row. Each 
barbule consists of a flattened process which appears 
to be twisted upon itself at about the middle of its 
length. Its proximal part has therefore the appear¬ 
ance of a flattened lamina and its distal of a filament, 
as owing to the twist the edge only is in the plane 
of the lamina. Now in the barbules of the distal 
series, the filamentous region bears a series of 
hooklets and slender processes which fit into a 
groove and notches developed in the lamina of the 
proximal barbules. Each set of distal barbules is 
thus hooked into a set of proximal barbules, so that 
each barb is locked to its neighbour. When the 
uniform surface of the feather vane is destroyed by 
forcibly separating the barbs, the hooklets are pulled 
out of the groove in which they lie. When the 
feather is restored to its original condition by 
smoothing with the fingers, the hooklets are slipped 
back into their original position. 
The barbs just described constitute the greater 
part of the vane of a quill-feather, but at the base of 
the vane there will usually be found a number of 
barbs of very different appearance. These are the 
downy barbs, and they are characterised by the fact 
that they are quite unconnected, and that their 
barbules are usually very long and slender, so as to 
be far more conspicuous than the barbules of the 
vane proper. These barbules bear no hooklets, the 
twisting is less obvious, and the appearance of length 
is given by the great development of the filamentous 
