Septa of bordering alveoli when lying in the plane of section exhibit pores at their outer margins closest to the plasma membrane. This shows that there is physical continuity between the lumens of alveoli. Basal bodies and fibrous systems are found in the cellular cortex beneath the ridges. Cacodylate buffered fixative. TEM taken on 11/2/68 by R. Allen with Philips 300 operating at 60kV. Neg. 20,500X. Published in J. Cell Biol. 49:1-20, 1971. Adapted with permission.