Typical organization of gap junctions as seen in thin sections (upper) and replicas of freeze-fractured cell membranes (middle and lower). Upper, gap junction from the saccular macula of a goldfish; middle, freeze-fracture preparation of a gap junction from a granulosa cell of the rat ovary; lower, freeze-fracture replica of a gap junction from the saccular macula of the goldfish. Images by K. Hama (upper, Fig. 93, lower, Fig. 95), and D. Albertini (middle, Fig. 94) 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.