Rapidly swimming cells, like the ciliated protozoa, offer an interesting opportunity to study the chemosensory behaviour involved in chemo-attraction/repulsion in response to external chemical stimuli. The membrane ultrastructure of ciliates resembles that of the chemosensory neurones and the olfactory epithelium in mammals (1 ). As in higher organisms, the cilia may have adapted a sensory role. Ciliates may therefore be viewed as “swimming receptors” where correlations between cellular behaviour, cell behaviour and molecular signal transduction events can be studied experimentally because many ciliates are easy to grow and handle in the laboratory.
