Replica of a freeze-fractured gap junction presents the inner half-membrane on one of the cells (P-face, lower half of the micrograph) and the the outer half-membrane of the other cells (E-face, upper part of the micrograph). Image by Daniel Friend is Figure 96 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.