The presence of a synaptic connection between neuron L7 of the abdominal ganglion and branchial ganglionic neurons (BGNs) was reexamined by means of electrophysiology and fluorescent microscopy using three Aplysia species. We succeeded in recording excitatory postsynaptic potentials produced in a BGN, which followed impulses of L7 one-to-one with a constant latency, even in A. californica as well as in A. kurodai and A. juliana. Dye-injection revealed that fine collaterals extended from a major branch of L7 to the branchial ganglion and arborized in neuropil of the ganglion. The results show that L7 in the three species has a dual function as a motor neuron and as an interneuron for the gill.