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the posterior cell is aligned along the long axis of the distributions of several asymmetrically localized proteins,1995; Chant, 1996; White and Strome, 1996). The timing and orientation of division contributes to the spatial organization of cells and thus can be important for morphogenesis, tissue organization and cellular interactions that influence developmental fate (Mello et al., 1994; Reinsch and Karsenti, 1994; Torres-Ruiz and Jürgens, 1994; Smith et al., 1996). Division orientation also plays a role in the segregation of cellular components during intrinsically asymmetric divisions (Strome and Wood, 1983; Chenn and McConnell, 1995; Kraut et al., 1996). In animal cells, division orientation is determined by the position of the mitotic spindle: the cleavage furrow always bisects the spindle (Salmon, 1989). Studies of oriented divisions in invertebrates suggest that astral microtubules interact with the cell cortex to position the spindle (Hyman and patterning in a multicellular organism. The pattern of ce division is virtually invariant from animal to animal, and th transparency of the organism facilitates examination o division pattern in living specimens (Sulston et al., 1983). Th embryonic division pattern is characterized by a series o unequal divisions. During the division of the one-cell, P0, th spindle is aligned along the longitudinal (anterior-posterior axis of the embryo and becomes positioned closer to th posterior pole. First cleavage is therefore unequal, giving ris to a larger anterior cell, AB and a smaller posterior cell, P1. A second cleavage, the P1 spindle is oriented on the same axis a the first spindle. At third cleavage, similar orientations are see in the daughters of P1 (EMS and P2). In both cells, the spindl pole is oriented towards the membrane furrow that separateINTRODUCTION In organisms ranging from yeast to mammals, certain cells have reproducible patterns of division during growth and cytoskeleton has also been demonstrated in algae and buddin