Cover legend: An afferent fiber in the posterior lateral line of a live zebrafish, labeled with the membrane-bound fluorescent protein mCherry under the control of a neuronal promoter, contacts a neuromast whose hair cells express green fluorescent protein. In this binary model of neuronal specificity, each axon synapses selectively with hair cells of only a single orientation, in this instance those responsive to ventrally directed water movements. For more information, see the article by Nagiel et al. in this issue (pages 8442–8453).