1. A reflex leg movement mediated by the prothoracic ganglion of Schistocerca is completely inhibited under most normal conditions but disinhibited if the ganglion is isolated from the C.N.S.
2. Progressive lesions to the C.N.S. give progressive disinhibition. The main inhibitory areas are the metathoracic, suboesophageal and mesothoracic ganglia.
3. The left and right sides of the thoracic ganglia are to some extent independent in both the transmission and reception of inhibitory signals. There is probably negative feedback between the reflex systems of the two sides of the prothoracic ganglion.
4. The inhibitory influence of a ganglion on the reflex appears to be proportional to its level of activity and to the amount of signal it is transmitting to the prothoracic ganglion. It is not constant, and is probably not mediated by a limited number of specific inhibitory tracts.
5. The general occurrence of similar mechanisms in animal nervous systems is suggested and discussed.