Figures 344 (upper) and 345 (lower) from Chapter 14 (Sperm Flagellum) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. Cross sections of the sperm tail of the Cecidomyid fly, Monarthropalpus buxi. Exceptional variation occurs in the organization of the sperm flagellum among species of gall midges, consisting of rows of doublets without any structure corresponding to the central pair in conventional axonemes. Image by R. Dallai, from Baccetti et al., Tissue Cell 6:269-278, 1974. A PDF copy of the accompanying chapter is available on the ASCB’s BioEDUCATE website.