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 

 booklets 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 booklets 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 booklets 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 booklets, the 

 twisting is less obvious, and the appearance of length 

 is given by the great development of the filamentous 



