A binucleated PL 1 Ut cell with broadly flattened lamellipodia fills the center of the field of view as the digital video initiates. Several other smaller fibroblasts adhere to its periphery, but as they migrate across the culture medium, the connections between them are gradually broken. The migration of PL 1 Ut cells and other fibroblasts involves extending and contracting lamellipodia and sometimes thin, narrow filopodia in a periodic fashion that produces crawling-like movements. As the surface protrusions reach out over the substratum, they form contacts with the surface that are used by the cells as anchorage points for contraction, which pulls the fibroblasts along their chosen paths. Sites of adhesion near the rear of the cell are released as each fibroblast continues to progress.

Located inside of the nuclei of the raccoon uterus fibroblasts are nucleoli, which are small, dense bodies that serve as sites of ribosomal RNA synthesis. Nucleoli contain RNA and protein, and are clearly observable through the use of both phase contrast and interference microscopy techniques. The powerhouses of the cell, mitochondria, are also visible utilizing such methods, and can be seen concentrated around PL 1 Ut cell nuclei during the high speed playback of the time-lapse sequence. The name of the organelles was coined based upon their appearance to scientists in the nineteenth century and was derived from the Greek words mitos and khondrion, meaning “thread” and “granule,” respectively.

Small pieces of cytoplasm left by fragmented cells are scattered across the imaging chamber. Some of the cell debris flows rapidly across the field of view, apparently carried away from the substratum by currents in the culture medium. Other cell fragments remain adhered to the surface of the chamber, at least until intact cells detect them and pass their ruffling lamellipodia over them. The active surface extensions are able to draw up the material as if they were tiny vacuum cleaners. The fibroblasts can then incorporate the newly gained bits of cytoplasm into their own cellular contents.