adjacent to adjacent to quadrant One of of four nearly identical quadrants organized along the oral-aboral axis. Each of the four quadrants is derived largely from one cell of the four-cell-stage embryo. At the eight-cell stage each quadrant contains a single E ("end") and M ("middle") blastomere. Subsequently, micromeres are formed first at the aboral pole and later at the oral pole. Two orthogonal planes run along the oral–aboral axis which define four quadrants (Fig. adesophageal plane tentacular plane slash quadrant backslash quadrant organism subdivision