Neurons in the first synaptic region of the bee, Apis mellifera.

Abstract

The retina-lamina projection in the visual pathway of the bee was studied by the reduced silver and Golgi techniques. Two main types of visual cell axons (R-fibres) were found: (1) at least two forms of short visual fibres terminate at two levels in the lamina; (2) the long visual fibres cross the first optic chiasma and terminate at two different levels of higher order neurons in the medulla. Six short and three long visual fibres leave each retinula in the bee's eye. Whereas two types of short visual cells can be distinguished by the arborization patterns of Golgi-stained preparations, as well as by their fibre diameters, three different types of long visual fibres can be found. In each cartridge (“neuroommatidium”) the six short visual cells closely appose three monopolar cells (L-fibres, second order neurons). Thus each axon bundle crossing the first (or intermediate) chiasma contains at least six large argyrophilic fibres (three long visual cells and three monopolar cells), and these can be seen in cross-sections of reduced silver preparations. In addition, centrifugal fibres originating in the medulla and terminating in the lamina as well as amacrine (intrinsic) cells of the lamina have been resolved by Golgi impregnation.