In D. melanogaster the cross-sectioned nerve of the leg-like antenna in the homeotic mutant Antennapedia was ultrastructurally compared with the nerves of the morphologically related second leg and the wild-type antenna. The nerves of the normal antenna and the second leg differ from one another in both the numbers and arrangement of axons. According to these criteria the nerve of the homeotic appendage was structurally identified as a leg nerve. Most of the antennal nerves studied showed a consistent grouping of axons in the profile. This suggests that the assemblage of the axons does not occur randomly, but in an ordered fashion.