Item

Abstract

Thanks to a technique of optical neutralisation associated with a transilluinination of the eye, it is possible to study the photoreceptor endings (rhabdomere tips) in the compound eye of live and intact Drosophilae.

The success of the neutralisation process directly confirms the idea that the convergence of the dioptric system in each ommatidium is essentially due to the refraction at the corneal outer surface. The remarkable regularity of the asymmetrical receptor pattern throughout the eye (fig. 7) is of functional importance. The divergence angle between the optical axis of neighbouring receptors, and their farfield radiation pattern are shown to depend respectively on the spacing and the diameter of the rhabdomere distal endings (fig. 8). The tip of the centrally located rhabdomere number 7 (fig. 5) is found to have a smaller optical diameter than its six neighbours and the extinction spectrum of this rhabdomere is different from those of the other ones. Modal patterns are observed at the distal tip of the rhabdomeres (fig. 9), confirming the waveguide properties of these components. The eye of Drosophila is morphologically composed of two equal parts, dorsal and ventral, in which the rhabdomere patterns are symmetrical (fig. 7). Sporadic irregularities are found in the border between these two parts (fig. 10).

Actually the main importance of this neutralisation technique lies in its possible applications. The simultaneous visualization of a lot of receptors, in transmitted light, allows a precise stimulation, in incident light, of single and known cells in the eye of live insects. This method combined with other in vivo techniques such as those using the phenomenons of “corneal pseudopupil” (Kirschfeld and Franceschini, 1968) and “deep pseudopupil” (Franceschini and Kirschfeld, 1971a) may simplify further studies regarding the nervous integration of visual stimuli in the facet eye.