Fig. 8. Leader axon alters midline kinetics of first contralateral axon at the midline during commissure formation. Single time point images showing stereotypic interaction between the initial POC growth cones. Two growth cones, one from each side, are visible with one already at the midline (left). Up to this point both growth cones have complex morphologies. Upon contact, however (middle panel), both growth cones change shape and become elongated (right) even though the second growth cone has not yet crossed the midline. When this second axon grows across, it has fast midline kinetics similar to a follower axon. Scale bar: 10 µm.