Phase contrast microscopy of living cells offers the ability to observe dynamic behaviors. This single frame image shows folds in the membrane at the periphery of a cell in growing in vitro. Asterisks indicate vacuoles associated with the pinocytosis of fluid from the extracellular environment. Image by Charles Pomerat, and published in Fawcett (1964) J. Histochem. Cytochem. 13:75-91, reprinted with permission as Figure 46 from Chapter 2 (Specializations of the Free Surface) 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.