Waves of excitation, visible as ciliary waves, pass along the elongated cells of the ciliated grooves to the comb plates. The frequency of waves is controlled by the loading of the statolith on the balancer cilia, which stand at the head of the grooves. They are primitive mechanoreceptor cilia. A beat of the balancer cilia is the initiation of a wave to the comb rows. All cilia in this sensory-conduction-effector line are marked by compartmenting lamellae. This is a distinct system superimposed on others in the animal, and reasons are given for suggesting that neuroid transmission in it will prove to be electrical transmission. This system is not anaesthetized by excess Mg++. Underwater ripple receptors set off a change in mood in which the animal turns over and swims downwards. There is a variety of modified cilia in the apical organ. Other responses such as the inhibition of the beat, mouth opening, feeding movements, and the protective withdrawal of the apical organ, are all co-ordinated by distinct and separate pathways which may prove to be regionally differentiated parts of one nerve net.