In the human oviduct epithelium during ciliogenesis, short tubular structures were found in the transitional zone between the basal body and cilium. The tubules, termed transitional tubules from their location, were 34–36 nm in diameter and 0.13±0.06 μm in length; the number around a basal body was variable, but usually 4–6. The cytoplasmic leaflets of the tubule membranes were coated by electron-dense material and appeared to be connected to alar sheets. The transitional tubules existed transiently during ciliogenesis. The exact role of transitional tubules is unknown, but considering their location, they may fix the basal body in the apical cytoplasm during ciliary elongation and/or may be related to formation of alar sheets.

The cell cortex of a ciliated protozoan contains most of the structure that defines the shape and pattern of the organism. The ciliate cell cortex is composed of both cytoskeletal and membranous components. While the assembly of the cytoskeleton is believed to account for the major part of the development of shape and pattern in this cell (as in all eukaryotic cells), the contribution of membranes to the development of cellular architecture in ciliates is poorly understood. Also, how the cortical membranes are assembled and how this assembly is coordinated with cytoskeletal assembly are virtually unknown. Furthermore, membranes have several unique properties which could be useful in the storage and utilization of blueprints for cellular architecture. Freeze-fracture and freeze-etch electron microscopy provide ways to characterize the molecular architecture and assembly of membranes during development. Efforts are being made to apply these methods to an analysis of morphogenesis and ciliogenesis in Tetrahymena. The results of these studies ar summarized and their possible implications regarding the role of membranes in ciliate morphogenesis are discussed.