Figure 232 from Chapter 7 (Mitochondria) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. Dividing mitochondria in gasric mucosa of a mole. Upper panel, the bilaminar septum as formed, but the outer membrane has not yet invaded the septum to complete fission (arrows). Lower panel, invasion by the outer membrane is not always a circumferential invagination of uniform width. In this image the center of the septum is separated by a deep and slender invagination from outside of the plane of section (star), while the outer membrane invagination within the plane has progressed only a short distance into the cleft (arrows). Image by Toku Kanaseki. A PDF copy of the accompanying chapter is available on the ASCB’s BioEDUCATE website.