Analysis of the effects of encystment and excystment on incomplete doublets of Oxytricha fallax.

Singlet cells of Oxytricha fallax possessing supernumerary rows of dorsally located marginal cirri were encysted, excysted, and observed for retention of the supernumerary rows. Without exception, cells lost the supernumerary rows as a result of cystment processes. (Encystment previously has been shown to result in the total resorption of ciliature.) In contrast, supernumerary dorsally located marginal cirral rows develop true-to-type during prefission morphogenesis and thus are inherited from cell to cell. These (and other) observations suggest that at least two levels of cytotactic control of cell patterning are operative on the ciliate cortex; one is dependent upon visible ciliature whereas the other is dependent upon an as yet ultrastructurally unidentifiable molecular architecture.