SYNOPSIS. The hypotrich ciliates possess a highly localized ciliature arranged in a predictable asymmetric and polarized fashion. They also possess a large repertoire of developmental alternatives, including morphogenesis of ciliature prior to fission, as well as during regeneration and reorganization. They also undergo a cystment process in which all visible ciliature dedifferentiates during cyst formation but redifferentiates upon emergence from the cyst. These organisms thus are highly suitable for analysis of cell patterning in eucaryotic unicells. Analysis of various types of experimentally induced cortical anomalies reveals that the final pattern of the cortex in these ciliates is determined by at least three distinct informational systems. Two of these systems are inherited cytotactically; one is independent of the presence of visible structure and provides information for the polarity and asymmetry of developmental fields as well as serving as a potential initiation site for a complete set of cortical structures, whereas the second is dependent upon visible ciliature and provides local information for structure-type and polarity of new ciliary structures. The third informational system, developmental assessment, operates coordinately with the other two and generates the final ciliary pattern of the morphostatic ciliate. Currently the molecular bases of each of these informational sets remain unknown.