Distribution of the stars in the Helmi streams in the XZ plane (i.e. perpendicular to the disc of the Milky Way), with the arrows illustrating their motions (amplitude and direction) in this plane. The symbols are colour-coded according to the amplitude of their V_Y velocity (i.e. perpendicular to the projected plane). Top and bottom rows: stream members with V_Z <  0 and V_Z >  0, respectively. Left and right columns: stars with V_X <  0 and V_X >  0, respectively. In all the four panels streaming motions and substructures are clearly apparent.