In a pennaceous feather, the barbs grow helically around the tubular feather germ and fuse on one side to form the rachis.Simultaneously, new barb ridges form on the other side of the tube.

在上，枝以螺旋绕著管状的芽生长，在管子的侧接合在成轴，同时在管子的另侧成新的枝脊。