Anatomy of the ocellar interneurons of acridid grasshoppers. I. The large interneurons.

The anatomy of the large ocellar interneurons in the brain of five species of acridid grasshoppers of two different subfamilies (Schistocerca vaga, S. gregaria, Gastrimargus africanus, Trimerotropis pallidipennis, and Arphia conspersa) was revealed by cobalt-filling of the three ocellar nerves and subsequent reconstructions from silver-intensified (Timm's method) serial sections. Conflicts in the literature are reviewed (Tables 1, 2) and differences in the number of cells, anatomical descriptions of these cells, and nomenclature are resolved by demonstration of an identical number of large ocellar identical number of large ocellar interneurons in all five species examined (Fig. 1). There are 17 large 1st-order ocellar interneurons (Figs. 2, 3). Each of the three ocellar nerves contains the axons of seven large interneurons; four of these interneurons have axons in two ocellar nerves. The anatomy of three pairs of 2nd-order ocellar interneurons (with branches in the ocellar tracts within the brain and axons in the circum-esophageal connectives) is reconsidered in light of recent conflicts in the literature. Previous accounts by Williams (1975) of interneurons O2, O3, and PI(2):5 are corroborated and new details added (Fig. 7) by the use of a cobalt method that appears to stain these 2nd-order interneurons transsynaptically (Fig. 6).