Two or more well-defined nuclei can be observed in each of several large A. P. Mongoose fibroblast cells. The large rounded objects in the nuclei are nucleoli, subnuclear structures unbound by membranes that manufacture the subunits of ribosomes. The rapidly moving granular-appearing material distributed throughout the cytoplasm around the nuclei is composed of mitochondria. The power generators of the cell, mitochondria were among the first organelles discovered, since they are large enough to be detected even by the light microscopes in use during the nineteenth century. The name of the organelles was coined to reflect the way they looked to the first scientists to observe them, stemming from the Greek words for “thread” and “granule.”

During careful examination of the high speed playback of the time-lapse sequence, vacuole formation can be perceived. Vacuoles rapidly are produced along an A. P. Mongoose cell’s leading margin (the fibroblast crawling diagonally from the mid right-hand side to the mid upper region of the field of view) and then are transported to the central region of the cell. In animal cells, the membrane-bound sacs are primarily utilized for temporary storage and transport of materials, such as bits of culture medium that can be digested to obtain nutrients. Vacuoles are formed via endocytosis, a process in which the plasma membrane invaginates to internalize foreign material.

The leading margin of A. P. Mongoose fibroblasts is generally the site where the extension and retraction of surface projections occurs most heavily. The broad, flattened projections called lamellipodia primarily function in fibroblast locomotion, whereas the narrow, finger-like projections known as filopodia can play a sensory role in the cell as well as facilitating movement. Note the wildly branching extensions seem to serve as feelers utilized by the cell to explore its environment. The rapid growth and pulling-back of lamellipodia and filopodia that gives the impression of a flickering light during the high speed playback of time-lapse sequences is called ruffling.