Ciliate Ultrastructure: Some Problems in Cell Biology*

Abstract

SYNOPSIS. Protozoology, along with other cell sciences, has profited immeasurably during the last 25 years from the application of electron microscopy and other new technics to studies of cell structure and function. Protozoa were among the first objects examined with the electron microscope in the 1940's and an extensive literature in protozoan ultrastructure has accumulated since then. Some examples of recent investigations of ciliate cortical ultrastructure are selected to illustrate the importance of protozoan studies to the development of fundamental concepts of cell biology. Ciliates are choice subjects for analysis of ciliary structure and motility and of myoneme contractility. Membrane‐limited alveoli contribute to the structure of the characteristic ciliate pellicle and provide evidence of how multiple pellicular membranes may affect cell‐surface activities. The striated fibrils and microtubules associated with ciliate kinetosomes resemble those of other cell types but are more highly organized; wherever they occur, these structures appear to be related to the development and maintenance of polarity and asymmetry of cells and organelles. Their stability and the precision of their arrangement in ciliates make them peculiarly suitable for the study of the properties and behavior of such fibrous organelles and also for investigation of the morphogenetic role of the kinetosome.

On Charles Atwood Kofoid (1865–1947): The good, the bad, and the ugly

“…Goldschmidt named the 'discovery' of the neuromotorium as Kofoid's greatest accomplishment (Goldschmidt 1951). The neuromotorium was not definitively put to rest until transmission electron microscopy studies showed the alleged sensory fibers to be structural and the absence of a point of convergence or a neuromotor organelle (Pitelka 1970).…”

“…Thus by the end of 1960's the fundamental studies of the existence of a neuromotorium (i.e., the structures described by Sharp in 1914) and a role in controlling ciliary coordination (i.e., reported by Taylor in 1920) had been discredited. The final nail in the coffin, so to speak, were transmission electron microscope studies of ciliates showing that "neuromotor fibers" were structural and no central organelle connected them (Pitelka, 1970). By 1973, the neuromotor apparatus was simply described as "now discredited" (e.g.…”