Item

Abstract

In the ommatidia of Musca, the light flux transmitted by each one of the rhabdomeres of sense cells no. 1 to 6 decreases as a function of time if light falls onto these rhabdomeres. With a similar time course the light flux reflected from these rhabdomeres increases. These changes take place within a few seconds following illumination. The results have been established in the intact animal using changes in the appearance of the pseudopupil as indicator and also in surviving preparations of the eye with direct inspection of the rhabdomeres.

The changes are interpreted as a consequence of interactions between pigment granules in the sense cells and electromagnetic fields induced outside the rhabdomeres by light travelling on the inside: In the dark adapted situation the granules are quite distant from the rhabdomeres, the interaction is negligible. During light adaptation the granules move close to the rhabdomeres, and as a consequence, total reflection of the light in the rhabdomere is frustrated. The relatively rapid changes in the optical characteristics of the rhabdomeres are explained by the fact that the distance, the granules have to move in order to switch from one condition to the other is in principle on the order of the wavelength of light.

The results indicate, that the changes in the position of the granules are induced by the excitation of the respective sense cells themselves, for instance by the degree of their depolarisation. No interaction between the sense cells of one ommatidium nor between those of different ommatidia could be found.

The function of the movement of the pigment granules is interpreted as a means to protect the sense cells no. 1 to 6 against strong illumination. — Movement of pigment granules is not induced in sense cells no. 7 and 8 with light intensities which give maximal response in sense cells no. 1 to 6.