To view this video please enable JavaScript, and consider upgrading to a web browser that supports HTML5 video Movie S4. Movie for Fig. 4B, showing posterior cells in a spheroid photostimulated from 3.92 s on the time counter at the bottom left. The arrow indicates the flagellum with a red arrowhead in Fig. 4B. The movie is run at ×1/17 speed. Detergent-extracted Volvox model exhibits an anterior–posterior gradient in flagellar Ca2+ sensitivity Noriko Ueki, and Ken-ichi Wakabayashi PNAS. 2018. 115:E1061-E1068 DOI: 10.1073/pnas.1715489115 Download Original Video Browse All Videos »