Pitzer College 1 article published in JoVE Biology Analysis of Motility Patterns of Stentor During and After Oral Apparatus Regeneration Using Cell Tracking Janet Y. Sheung1, Megan Otsuka2, Gabriella Seifert3, Athena Lin4, Wallace F. Marshall4 1W. M. Keck Science Department, Scripps, Pitzer, and Claremont McKenna of The Claremont Colleges, 2W. M. Keck Science Department, Pitzer College, 3W. M. Keck Science Department, Scripps College, 4Department of Biochemistry and Biophysics, School of Medicine, University of California at San Francisco We present a protocol for the characterization of motility and behavior of a population of hundred micron- to millimeter-sized cells using brightfield microscopy and cell tracking. This assay reveals that Stentor coeruleus transitions through four behaviorally distinct phases when regenerating a lost oral apparatus.