The author observed the effect of stimulation of the closing muscle of claw of some crabs (Portunus trituberculatus, Goetica depressus and Serama haematoheir) with galvanic or induction currents. The results obtained may be summarized as follows: 1) It was observed that the movements of claw occur rapidly or slowly according to the strength of the stimulation, id est strong or weak respectively. Intermediate type between the above desribed movements was never observed. The two distinct types of movements were demonstrated clearly in Goetica depressus and Serama haematoheir, but in Portunus trituberculatus a slow movement was not distinct. 2) Repetitive stimuli were more effective than a single stimulus, and the number of the most effective ones was 4-6per sec. 3) The mode of movements was not influenced by the duration and the repetition of stimulus. But a rapid movement was apt to accur through a stimulation of short duration and high frequency. 4) The above obtained results may be easily understood under the supposition that there is two sorts of nerve and muscle, i.e. the one set has a low threshold of excitability and responds with slow contraction, whereas the other has a high threshold and responds with quick contraction.