An analysis of the mechanism of the jumping organ of the cylindrical springtail Tomocerus longicornis and the globular springtail Dicyrtoma ornata is presented based on morphological examination and high-speed photography. Both species have a click mechanism involving deformation of the abdominal sclerites. Morphological and photographic evidence supports the hypothesis that eversion of the springing organ involves a hydroelastic mechanism based on haemocoel pressurization and increased tension in the abdominal sclerites. A computer model was used to analyse jump kinematics and energetics. This model accounts for the spin observed during jumping and shows how body planform (e.g. cylindrical versus globular) and tail length can influence direction, height, range and rate of spin.