Variability in caudal advance of individual ENCCs. A. Cells that were 600 to 700 μm from the wavefront (white arrow) were photoconverted. B. Some photoconverted cells migrated caudally along existing strands with high speed and directionality (cells “a” and “b”, white and aqua tracks), and nine hours later, one of the cells (cell a) was very close to the wavefront; cell “a” migrated 980 μm in nine hours before going out of the field of view. Cell “a” (white track) also reversed direction and migrated rostrally for one hour, before migrating caudally again (white open arrow). C’. Another cell (arrow in C’) was imaged for 16 hours. C. This is an enlarged image of C’ with a color time track showing that it exhibited a complex, circular pathway; despite migrating at 70 μm/h, it advanced caudally only 140 μm after 16 hours. D. A red channel only showing a photoconverted cell (asterisk) that continues to advance caudally after it is first rounded up (arrow). E, F. Local leapfrogging at the migratory wavefront. E. The most caudal cell (yellow arrow) at the commencement of imaging was photoconverted. F. Ten hours later, the cell (yellow arrow) was > 200 μm behind the most caudal cell. Caudal advance was defined as the longitudinal caudal displacement of an ENCC during the imaging period regardless of its pathway; this cell advanced caudally only 70 μm in 10 h. The other red cells in this image are photoconverted cells that were out of the field of view (rostral) at the beginning. G-I. Correlations for the entire ENCC population shown in Figure 1 between speed and angle (G), caudal advance and angle (H) and caudal advance and speed (I). R2 is the correlation coefficient. A negative value for the rate of caudal advance means that the ENCC moved rostrally during the imaging period. ENCCs, enteric neural crest-derived cells.