A high resolution image of the cortex of Didinium nasutum. Embedded within the fibrous layer are many extrusive organelles, called mucocysts, involved in cyst formation. In this view there is also a longitudinal section of a more prominent and long curved extrusome (called a cyrtocyst by Wessenberg and Antipa, 1968) in the proter of a dividing cell. The cyrtocyst is of unknown function. Extrusomes of Didinium typically have a bundle of myelin-like membrane material enclosed by their surrounding membrane. This may be stored membrane needed for extrusome discharge. TEM taken on 5/20/69 by R. Allen with a Philips 300 operating at 60kV. Neg. 14,800X. The raw film was scanned with a Nikon Coolscan 9000ED. 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/).