Fig. 1. Handedness of embryonic and adult asymmetries. Colored letters A, P, D, V, R and L indicate anterior, posterior, dorsal, ventral, right and left, respectively. (A) A dextral (normal) adult hermaphrodite viewed ventrally, showing asymmetric placement of the gonad (g), intestine (i), excretory cell (xc), coelomocytes (cc), and the traverse around the vulva (v) of the ventral nerve cord (nc). (B) Cell positions and spindle orientations before, during, and after the second AB cleavage. AB cells are colored gray. No LR asymmetry is apparent at the four-cell stage. In ventral view, the EMS cell (broken circle) lies above the ABa and ABp cells. As ABa and ABp enter mitosis, their spindles (arrows) are oriented parallel to the LR axis. The spindles then skew as shown, always in a counter-clockwise direction (from this vantage point), so that the resulting daughter cells ABal and ABpl are shifted anteriorly relative to their respective sister cells ABar and ABpr, giving the embryo LR asymmetry with the dextral handedness that is maintained throughout development.