Cover legend: Re-colored and stylized light micrograph of the ventral aspect of a segmental ganglion of the medicinal leech. Individual neuronal somata are visible. Each segmental ganglion of the leech CNS contains a complete neural oscillator for crawling. For a discussion of the mechanism for coordination of the segmental crawl oscillators, see the paper by Puhl and Mesce in this issue (pages 2373–2383).