Afferent neurons traverse projections that extend to mature synapses. (A) An SBEM reconstruction shows a hair cell projection (green) extending into an aggregation of variously colored axonal terminals beneath mature ribbon synapses made by another hair cell (yellow). (B) In a frame from a time-lapse sequence, a projection (arrowhead) extends toward a presumptive ribbon synapse (asterisk). (C) A series of time-lapse confocal images shows extension of an afferent terminal along a projection (arrowheads). Times are denoted in minutes after rearrangement. (D) A reconstructed afferent terminal (magenta) traverses a hair cell projection (cyan). (E) An SBEM reconstruction demonstrates that all neurons contact the nascent cell soma on its two projections (asterisks). (F) Projections arising from anteriorly and posteriorly polarized hair cells make the greatest areas of contact with afferent neurons of the same polarity. P < 0.02; N = 4. (G) An unusually large projection (arrowhead) forms in the absence of lateral line neurons. (H) The reconstructed sibling hair cells from a larva whose lateral line ganglion had been ablated exhibit numerous and lengthy projections. (I) In the absence of lateral line neurons, projections show reduced stability. P < 0.01; N = 12 and 11.