Fig. 4. An example of retrograde movement for XBX-2::GFP particles in a phasmid cilium (see also Movie 1 in supplementary material). The ciliary transition zone is marked with an asterisk. The arrowhead indicates the initial position of the moving particle at time zero (t=0). The arrow indicates the position of the moving particle at different time points (t=0.5 and 1 seconds). Scale bars: 1 µm.