Freeze fracture replica of zonula occludens junctions from the small intestine of a Xenopus laevis tadpole. The occluding junction appears as a meshwork of ridges on the P-face or a corresponding pattern of grooves on the E-face. The geometric patterns of ridges and grooves vary depending on the epithelium. Image from Hull and Staehelin, J. Cell Biol. 68:688-704, 1976, and reprinted with permission as Figure 64 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.