The spiral cleavage pattern. (A) Animal pole view of a generalized spiral-cleaving embryo. Arrows indicate the direction of cell divisions. Developmental sequence based on (Conklin, 1897). (B) Schematic diagram of cell divisions in the D quadrant in a lateral view (top: animal pole, bottom: vegetal pole). Cells are named with the standard spiral cleavage notation(Child, 1900; Conklin, 1897; Wilson, 1892). Representation based on Lambert (2010).