The ultrastructure of Herbst corpuscles in the lingual mucosa of the finch, Lonchura striata var. domestica, was examined by light and electron microscopy. Numerous Herbst corpuscles were found at the top of connective tissue papillae just beneath the dorsal epithelium. The Herbst corpuscle was composed of an outer capsule, inner core and central axon. The central axon was discoid in shape and immunoreactive for NSE-antiserum. The central axon was surrounded by compactly stacked layers of thin lamellae of lamellar cell processes. Since these lamellae did not completely encircle the axon as seen in cross sections, they displayed a symmetrical longitudinal cleft dividing the inner core into bilateral halves. Numerous axonal spines were seen to extend from the Y-axis of the axolemma into the cleft and occasionally into the cytoplasmic invagination of the lamellar cell body in the inner core. A number of clear and dense-cored vesicles were seen in the axoplasm near the base of axonal spines. Further, the omega-shaped coated invaginations were occasionally found on the axolemma near those places. These findings suggest that the area nearby the axonal spine in the central axon of the Herbst corpuscle is a site active both metabolically and functionally.