SYNOPSIS. In many hypotrich ciliate protozoa there are at least 6 possible categories of ciliary structures: right marginal cirri, left marginal cirri, fronto‐ventral‐transverse cirri, membranelles, and 2 oral membranes. This report describes the kinetosomes, fibrils and microtubules which make up the cytoplasmic portion of these structures in Gastrostyla steinii.
Altho light microscope studies have revealed significantly different infraciliature for the 3 classes of cirri, the fine structure of these locomotor organelles indicates that they have a remarkable number of homologous structures. There is also a number of apparent homologies between the cirri of this organism and ciliary structures of both more primitive and more highly evolved ciliates. The oral ciliature of G. steinii is analyzed and compared to that of other spirotrichs for clues to the phylogeny of the hypotrichs. Function of the infraciliature is considered briefly.