As if they were enjoying a slow dance with one another, a pair of CV-1 epithelial cells spins around the field of view in a lingering manner. The migratory movements of the cells are dictated by expansion and contraction of their surfaces. The flattened lamellipodia that extend around each of the cells are most active in areas where the cells do not overlap. The wave-like motions created by the erratic stretching out and pulling back of lamellipodia is called ruffling. During the high speed playback of time-lapse sequences, ruffling membranes can give one the impression that they are seeing a flickering light in the field of view.

The actin cortices of the cells dictate the local expansion of their surfaces. Located directly beneath the plasma membrane, the actin cortex is generally free from membrane-bound organelles and sometimes has a glassy appearance when viewed under a microscope. Significant changes in the polymerization of actin present in the cortex are generally accompanied by major shifts in cell shape. A number of associated proteins bind to actin and greatly impact filament behavior.

Vacuoles are membrane-bound sacs that in animal cells primarily function in the temporary storage and transport of materials. The endocytic formation of vacuoles can be observed both in the pair of previously mentioned CV-1 cells and other cells that migrate in and out of view along the right. Notice that the small, circular vacuoles appear first at the periphery of the cells and then travel to more central areas. The sacs probably contain culture medium and are transported to locations within the cells where they can be digested to provide nutrients essential to their survival in culture.