1. The connexions of single, identified motor neurons have been studied in the thoracic ganglia of the cockroach, Periplaneta americana. Selected cell bodies were identified on purely morphological criteria from one animal to another. Similarly, serially homologous cell bodies were identified from one ganglion to another. Their connexions to particular limb muscles were demonstrated by intracellular stimulation through the cell body and infsequent marking with procion yellow dye.
2. Serially homologous cell bodies in the mesothoracic and metathoracic ganglia innervate serially homologous muscles in the mesothoracic and metathoracic limbs.
3. Metathoracic limbs transplanted to the mesothoracic segment retain their metathoracic characteristics. They become functionally incorporated in the mesothoracic segment and are used normally during walking movements.
4. These transplanted metathoracic limbs become re-innervated from the mesothoracic ganglion. Identified mesothoracic cell bodies make specific connexions with those metathoracic muscles which are the serial homologues of their own muscles.