Figure 8.

Development of the PLL between 6 and 42 hpf. The vertical arrows indicate the times when the corresponding structures can be unambiguously identified either microscopically or, in the case of the PLL precursors, because of the end of retinoic acid dependence and the onset of mitotic quiescence. No arrow has been drawn for the secondary neurons (neurons II) although indirect evidence based on regeneration experiments suggests that they begin to differentiate around 32 hpf. placI, Primary placodes; placII, secondary placodes.