Journal of Cell Science, Vol 13, 663-675, Copyright © 1973 by Company of Biologists

Submitted on April 9, 1973

Cyclic Membrane Flow in the Ingestive-Digestive System of Peritrich Protozoans

I. Vesicular Fusion at the Cytopharynx

¹ Department of Anatomy, University of Wisconsin, Madison, WI. 53706, U.S.A.; Department of Anatomy, Upstate Medical Center, Syracuse, New York 13210, U.S.A.

Food vacuoles in peritrichs form by pinching off the distal half of the cytopharynx; and thus the pharyngeal membrane must be renewed during feeding. Correlation of light- and electron-microscopic observations indicates that the membranes of the ingestive-digestive system recycle. As the young food vacuoles enter the first stage of digestion (condensation of the vacuole), they pinch off cup-shaped coated vesicles which, in association with the microtubular post-oral fibres, return to the pharynx. In the peripharyngeal region, the 0.25-µm diameter cups flatten into 0.42-µm diameter disks, which then fuse with the pharyngeal membrane, thereby providing membrane for future food vacuoles. Ultrastructural evidence for similar patterns of cyclic membrane flow and the functional implications of the association of the pharyngeal membrane with the microtubules of the pharyngeal ribs are considered for other protozoa, including suctorians.