High resolution image of the cytoproct is the site of spent vacuole defecation on the surface of Paramecium. When closed the cytoproct forms a long narrow wavy ridge along the posterior suture. At its apex the ridge is about 0.2µm wide and it can be as much as 12µm or more in length. This ridge has the ability to be pulled down against the approaching spent vacuole where the plasma membrane covering the midline of the ridge will meet and fuse with the membrane of the vacuole. The ridge contains unique fibers on both of its lips that mesh with each other as they meet inside the ridge (see Allen and Wolf, J. Cell Sci. 14:611-631, 1974). TEM taken on 4/19/79 by R. Allen with Hitachi HU11A operating at 60kV. Neg. 10,000X. Bar = 0.5µm. The raw film was scanned with an Epson Perfection V750 Pro. This image is best used for quantitative analysis. Standard glutaraldehyde fixation followed by osmium tetroxide, dehydrated in alcohol and embedded in an epoxy resin. Microtome sections prepared at approximately 75nm thickness. Additional information available at (http://www5.pbrc.hawaii.edu/allen/).