A long, thin tail-like structure, termed a retraction fiber, can be observed trailing behind many migrating Madin-Darby bovine kidney cells. Retraction fibers exhibit contractile properties. Sporadically the thinly stretched strands of cellular material are pulled away from the substratum and contract back into the main process of the cell to which they belong. When this occurs, there is also typically a corresponding bout of heavy lamellipodial action along the anterior margin of the cell.

Lamellipodia are utilized by epithelial cells to locomote and are comprised of sheets of membrane-enclosed cytoplasm. Extension of lamellipodia over a substratum occurs in a fluid fashion. As can be observed during the high speed playback of the time-lapse sequence, lamellipodial activity is reminiscent of the periodic rolling in and out of the ocean tide. The overall movement of lamellipodia is toward the posterior of a cell, the surface structures continually flowing backward in a phenomenon known as ruffling.

In each of the MDBK cells, one or more nuclei can be clearly discerned. Within the nucleus, nucleoli can be observed, and concentrated around the important organelle are numerous mitochondria. Note, mitochondria are not static entities, as they sometimes seem to be portrayed in textbooks, but are rather dynamic organelles that carry out significant intracellular movements. The migration of mitochondria is largely governed by microtubules, one of the three major classes of cytoskeletal filaments.