Feather barbules. Coloured scanning electron micrograph (SEM) of barbule hooks on a feather from a bird. The flat broad vane of a feather is formed by comb-like rows of filaments called barbs, which project from either side of a central shaft. Each barb has rows of minute filaments called barbules, the barbules on one side bear hooks, while those on the other have a groove. The arrangement is such as to hook adjacent barbs together, interlinking the whole structure. Thus the feather is strong, yet still flexible and lightweight, making it ideal for flight. This feather is from a swallow (Hirundo sp.). Magnification: x1270 when printed 10cm wide.