Ultrastructure of the Herbst corpuscle from beak skin of the pigeon.

In serial sections of the lamellar sensory Herbst corpuscle from beak skin of the domestic pigeon the authors followed the change in the ultrastructural picture in sections led at different levels of the corpuscle. In the proximal part of the corpuscle the inner core is formed by only a small number of broad lamellae whose number subsequently increases so that in the middle of the length there are much more lamellae and they are quite narrow. This situation is probably given by the fact that the lamellae of the inner core gradually "unwind" from the plasma of Schwann cells in distal direction. In order to judge the ultrastructure of sensory corpuscles it is necessary to have serial sections through the whole corpuscle or at least its greater part. In cross sections of the corpuscles it is visible that as a rule projections of Schwann cells reaching up to the axon are lying between the lamellar systems, forming in this way two interlamellar spaces. However, in some sections there are only collagen fibrils in one of the spaces. Ir reminds of the cleft in Pacinian corpuscles. The authors are therefore of the opinion that this phenomenon is caused by a proximodistal shift in the arrangement of Schwann cells of both sides in non-Lamellirostres. This space probably represents the boundary between the lamellar systems of neighbouring Schwann cells of one side. The study further confirmed the incidence of large dense core vesicles in the plasma and projections of Schwann cells. Their diameter ranges between 150...200 nm. The character of these vesciles, which also correspond to Merkel granules, may be explained by ultrahistochemical examination. Oblique sections through the lamellae of Schwann cells could imitate the incidence of sympathetic nerve fibres between the lamellae of th inner core or in neighbourhood of the axon, as stated by Santini. Finally, in one section at the very beginning of the corpuscle, the authors observed in close neighbourhood of the central axon a formation whose structure resembled a vegetative nerve fibre. However, its existence was not found in further sections. Evaluation will be possible only after gathering more material.