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"Fig. 21. -A single barbule, baring barbicels and hooklets; magnified; after Nitzsch. ...barbicels (another dimin. of barba), also called cilia, or lashes (fig. 21); and hamuli, or hooklets (Lat. hamulus, a little hook; fig 21). These are simply a sort of fringe to the barbules, just as if the lower edge of the barbules were frayed out, and only differ from each other in that barbicels are plain hair like processes, while hamuli are hooked at the end; they are not found on all feathers, nor on all parts of some feathers." Elliot Coues, 1884

Single Barbule

"Fig. 21. -A single barbule, baring barbicels and hooklets; magnified; after Nitzsch. ...barbicels (another…