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。