Occluding junctions in Sertoli cells of ram and rat testis. Multiple focal sites of membrane fusion are indicated by arrows in each panel. Underlying these sites, associated bundles of filaments and typical subsurface cisternae are apparent in panels A, B and D. A, B, C from Gilula, Fawcett and Aoki, Dev. Biol. 50: 142068, 1976; D, Dym and Fawcett, Biol. Reprod. 3: 308-26, 1970; Inset from Wade and Karnovsky, J. Cell Biol., 60:168-91 illustrates two models regarding the relationship between the two cell membranes at these junctions. Regions indicated by asterisks in the micrograph in panel C support model "A." Micrographs reprinted with permission as Figure 69 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.