In the upper right-hand corner of the field of view as the digital video commences, a spherical 3T3 parent cell prepares to undergo mitosis. Only one of the daughter cells can be observed following the process, but the characteristic post-mitotic flattening of the fibroblast can be clearly seen. The flattening occurs as large, fan-shaped lamellipodia are formed. The more fluid region of cytoplasm near the center of the cell, called plasmasol, streams into the growing surface extension, reducing the thickness of the cell’s body. Thin, finger-like filopodia also form and appear to be used by the cell to explore its environment before it crawls out of the field of view.

Subsequently, several other cells actively migrate into the field of view and divide, including a triplet of fibroblasts that undergo mitosis in quick succession near the end of the video. Each new daughter cell soon assumes its own polarity and begins to travel in a disparate direction. As lamellipodia and filopodia recede, the plasmasol contained inside them streams back into the body of the cell, and can then be used to produce extensions in alternate locations on the cell’s surface. Along the leading edge of each cell significant ruffling occurs as lamellipodia are repeatedly drawn up from the culture medium and move toward the rear of the cell, eventually collapsing like waves breaking on a shore.

When the field of view clears about midway through the time-lapse sequence, the low volume of cells allows for an excellent view of the basic shape freely migrating fibroblasts tend to assume. As demonstrated, the leading margin is generally comprised of well-spread lamellipodia and is, therefore, broad, similar to the side of a triangle. Two other sides of a triangle can be considered to be formed by the other portions of the cell, which project backwards from the anterior end of the moving fibroblast and taper into a narrow tail. Known as a retraction fiber, the tail periodically releases its grip on the substratum and contracts back into the cell.