The response of Vorticella convallaria to electrical and mechanical stimuli was investigated. It was shown that: (I) V. convallaria becomes habituatcd independently to both mechanical and electrical stimuli if these are repeated at I0 sec. intervals. (2) The habituation is more rapid to lower intensities of stimuli. (3) The form of the response curve is similar for both types of stimulus. (4) No habituation was obtained when the animals were stimulated while in deionized water. No response was obtained while they were placed in a solution of CaCl2 but continuous contraction was induced in a solution of KOH. Other potassium and sodium salts in deionized water gave response curves similar to those obtained under normal conditions.