Gap junctions isolated from mouse liver and negatively stained with uranyl formate. At higher magnification, the 8-9 nm particles, or connexons, have a central 1.5-2 nm electron dense pore. Images by Bernard Gilula appear as Figures 97 (upper) and 98 (lower) from Chapter 3 (Junctional Specializations) 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.