Scanning electron micrograph of the surface of a peritoneal mast cell from mouse shows undulating folds, and few microvilli. The membrane folds could be misinterpreted for microvilli if analyzed in thin sections using a transmission electron microscope. Image by Emma Shelton, Figure 37 from Chapter 2 (Specializations Of The Free Surface) 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.