The ciliated organ of asymmetry in the zebrafish embryo. Fluorescent labeling of apical membranes (red) demarcates the lumen of this spherical organ called Kupffer’s vesicle. Motile cilia (green) projecting into the lumen generate an asymmetric fluid flow that orients the left-right axis of the embryo. Image taken by Jason Gokey. For more information see Jeffrey Amack, this issue.