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.

在正上，螺旋形绕著管状的芽生长，在管子的一在一起形成轴，同时在管子的另一形成新的脊。