In insect spermiogenesis, mitochondrial cristae disappear and a proteinaceous material is deposited in filaments that become closely packed paracrystalline arrays. In this micrograph, crystals are present in each of the two mitochondrial derivatives that flank the axoneme in spermatozoa of the stilt bug, Jalysus. This image, courtesy of David Phillips, appears as Figure 252 from Chapter 7 (Mitochondria) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. A PDF copy of the accompanying chapter is available on the ASCB’s BioEDUCATE website.