A high resolution image of the cortex of Paramecium consists of a plasma membrane and alveolar sacs, with their inner and outer alveolar membranes that limit the area in which endocytosis can easily occur to only the parasomal sacs. Parasomal sacs are cylindrical indentations of the plasma membrane that pass through the alveoli, not by penetrating through the sac but by passing through the septum. A short branch of the septum passes around the parasomal sac. In some areas the parasomal sacs extend almost perpendicularly from the basal bodies (not shown in this micrograph). There is one parasomal sac per surface depression in non-dividing cells. Rough ER, mitochondria, peroxisomes, trichocysts, and kinetodesmal fiber stack are seen in this image. The cell was incubated in hydrogen peroxide and diaminobenzidine to label the peroxisomes. TEM taken on 2/27/81 by R. Allen with Hitachi HU11A operating at 75kV. Neg. 10,250X. The raw film was scanned with a 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/).