Fig. 6. Formation of stitches. (A) Four consecutive stitches of the L-PLL line. The axons innervating the different neuromasts of one stitch are most likely collaterals of the same axons that innervated the founder neuromast. (B) The first step in the formation of a stitch: a small neuromast comprising only one differentiated hair cell has formed about 50 µm away from the founder neuromast, to which it remains connected by axons (arrowheads). Inset shows a magnified, contrast-enhanced view of the axons connecting the two neuromasts (arrowhead). (C-H) A series of stitches of increasing sizes. As judged from this series, and from the branching pattern of the collaterals, stitching occurs by a succession of budding events, each of which generates one (or at most two) additional neuromast. The arrows point to axonal bifurcations that presumably reflect budding events. The asterisk marks the common root of the innervating fibres. All panels represent stitches at the caudal level of the L-PLL except A,B, which illustrate stitches at the pectoral level; thus, the asterisked axons in B are directed dorsalwards, whereas in C-H they are directed anteriorwards. Scale bar for B-H is shown in E. Anterior is towards the left and dorsal is upwards.
