Ultrastructural analyses of arthropod epithelia revealed that cell membranes appear connected by ladder-like “bridges” or septa, hence called septate junctions, which localize basal to the zonula adherens (Figure 1A). The strands of the SJs exhibit different characteristic features both near and at TCJs. SJ strands between two cells change their course and align parallel to the junction between the three cells (Figure 1B). The most central strands (limiting strands; Figures 1B and 1C, green) are joined by a series of regularly spaced bridges, which were inferred to be composed of an extracellular “diaphragm” (Figures 1B and 1C, orange) associated with the three linked cell corner membranes. The extracellular space between the three apposed cell corners is very small, as the limiting strands are separated by 25–40 nm. – Dev. Cell 33: 501–503.