A new technique using a stimulating chronically-implanted electrode has allowed us to study the motor responses induced by electrical stimulation of the optic lobe in a freely swimming Sepia. Electrical stimulation of the cortex of the optic lobe produces no motor response; this is in agreement with the results of preceding authors. The stimulation of the neuropil of the optic lobe by monopolar electrode produces many different motor responses, in support of Boycott's results obtained by the same type of excitation in acute experiments. However, the field of stimulation of these electrodes could not always have been the same and it is possible that we were sometimes stimulating nervous structures close to the optic lobe. Stimulation by a bipolar electrode, however, which does not have this advantage, induces only two very different motor responses: an ipsilateral rotation and an 'alarm reaction", so called because of its similarities to the 'attentive immobilization" of higher vertebrates. These two reactions are very complex and their different components are linked together as in a behavioural response from an intact animal. These reactions present very different characteristics of excitability. They are obtained from many areas in the neuropil of the optic lobe, within which there does not seem to be any preferential localization. These results emphasize the importance of the optic lobe in motor control.