The Structure and Function of the Insect Dorsal Ocellus

Abstract

Publisher Summary This chapter focuses on the gaps in the knowledge of the physiological properties of the ocellus. By indicating current areas of interest, the deficiencies may be made good and the possibility of an ocellar contribution may automatically be considered when any visual dependent behaviour in insects is being examined. It is now fairly clear how the ocellus functions as a photoreceptor; it signals phasic and tonic information about intensity levels to the brain. Ocellar structure, with the dioptric system forming an image outside the retinal layer and a high degree of convergence on to second order neurons, suggested such a function to earlier workers and physiological information has brought confirmation. So far all ocelli have been found to signal in the same way with light modulating a dark discharge in the ocellar nerve via a first order inhibitory junction. Recordings made from the ocellar nerve have probably all been from the larger fibres and the properties of the small fibres present in some cases are unknown. The electrical activity of the retinular cells and their axons and the inhibitory junction with the second order neurons are of intrinsic interest, especially since evidence of first order inhibitory synapses is accumulating from other arthropod photoreceptors.