The origin of mirror-image symmetry doublet cells in the hypotrich ciliateParaurostyla weissei.

Mirror-image doublets of the hypotrich ciliateParaurostyla weissei were induced by modifying culture conditions. Successive steps of doublet formation involve inhibiting the separation of daughter cells during cell division and the shifting of these to attain a parallel configuration. The posterior part of the adoral band of membranelles in the right component then turns to the left and fuses with the distal terminal of the membranellar band in the left component. In effect, part of the adoral band and some of the paroral membranelles become apposed upside down, and the paroral membranelles of the right component are located on the left side of the adoral membranelles. A new site of oral primordium formation is initiated at the junction of the two oral apparatuses, the ciliature of which is arranged in a mirror-image pattern. During further cortical reorganization, the whole body ciliature of the right component becomes organized as a mirror-image of the normal left component.Both components of the doublet show the same ultrastructure of body ciliature and lack the right marginal cirri; the symmetry-reversal half, however, possesses multiple rows of left marginal cirri. The individual adoral membranelles and paroral membranelles in the symmetry-reversal component are rotated anteroposteriorly. Some aspects of the patterning of cortical structures are discussed.