1. The roots of the segmental nerves in nymphs of Anax imperator originate from separate dorsal and ventral tracts in the ganglionic neuropile.
2. Axons forming the dorsal part of the nerve root can sometimes be traced to ganglion cells and tend to be large and thick-walled compared with the ventral axons which are smaller and thin-walled.
3. In the roots of the fifth nerves of the last ganglion the two parts can be separated by dissection. Recording from each part under various conditions of stimulation shows that sensory activity occurs predominantly in the ventral part of the nerve root whilst motor spikes are recorded almost entirely from the dorsal part.
4. It is concluded that there is a functional localization of motor and sensory fibres in the root of an insect nerve comparable to that in the dorsal and ventral roots of vertebrate nerves.