Skeleton representation of moving cells. A. The skeleton of a closed region is obtained by finding bitangential circles throughout the cell (three are shown in green). The centers of these circles (black dots) are joined to form the skeleton (red line segments within the region). B. Fluorescent image (B1) of a wild-type Dictyostelium cell chemotaxing towards the bottom along with the computed skeleton (B2) and overlay (B3). C. Similar representation for a DIC image. Scale bars represent 5 μm.