The first optic ganglion of the bee VI: A sexually dimorphic receptor-cell axon

The characterization, distribution, arrangement and branching pattern of the retinal receptor-cell endings in the first and second synaptic region, the lamina and medulla, were studied in various regions of the compound eye of the drone bee. Light- and electron-microscopical Golgi techniques were applied in these investigations. 1) The nine receptor cells in each ommatidium of the drone bee — like in the worker bee (Ribi 1974, 1975, 1979) — end as six short visual fibres (two svf1, two svf2, two svf3) in the lamina, and as three long visual fibres (lvf 1, 2, 3) in the medulla. 2) In the frontal dorsal region of the eye the four receptor cells known to terminate either as svf2 and svf3 axons, respectively, display — in this particular region of the eye — one and the same distinct type of short visual fibre (svf4). 3) This sex-specific short visual fibre shows a highly branched axonal ending, which reaches the proximal part of stratum A. The numerous laterally arranged sidebranches interweave with the nerve fibres of the cartridge and are presynaptically connected with mainly L1 and L2 interneurones. 4) The sex-specific receptor type is found in the field of view where the diameter of ommatidial lenses shows a maximum and which is used while chasing the queen