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.
正,以螺旋形绕著管状的芽生长,管子的一侧一起形成轴,同时管子的另一侧形成新的脊。
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