Most wild type Tetrahymena have a macronucleus and a micronucleus. The micronucleus, seen here, is essentially nonfunctional during interphase. Its function is to replicate and pass a complete copy of the genome to each daughter cell and to give rise to a new macronucleus following sexual reproduction. Many laboratory strains, unlike strain W which is shown here, have lost their micronucleus and seem to be able to live indefinitely without a micronucleus, however, they can no longer undergo meiosis and sexual reproduction. TEM taken on 4/8/65 by R. Allen with RCA EMU3F operating at 50kV. Neg. 9,100X. Bar = 0.5µm. The negative was printed to paper and the image was scanned to Photoshop. This digitized image is available for qualitative analysis. An unprocessed, high resolution version of this image (CIL:34534) is in the library and available for quantitative analysis. Additional information available at (http://www5.pbrc.hawaii.edu/allen/).