A thin section through a macrophage from interstitial tissue of the testes of the opossum. These cells are characterized by extensive folding of the cell surface, some of which appear to have captured fluid from the extracellular environment through pinocytosis. Figure 50 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.