Microanatomy of the anterior median eyes and its possible relation to polarized‐light reception inLycosa tarentula(Araneae, Lycosidae)

Abstract

Abstract Microanatomy of the anterior median eyes (AME) of a lycosid spider (Lycosa tarentula) shows two classes of photoreceptors in the retina: dorsal and median visual cells (A) are polygonal in cross‐section and bear rhabdomeres on all their faces; ventral visual cells (B), rectangular in section, bear rhabdomeres only on two opposite faces; rhabdomes are aligned in parallel series and successive lines of rhabdoms are oriented orthogonally to each other. Receptor A cells are wider than ? cells, and about twice as numerous. In AME optic nerve, axons are also of two types, large and small, and the optic centre shows thick and narrow fibres, from the second order neurons, being separated by connective and glial cells. Anterior median eyes of second stage juveniles already present the same structure as those of adults. A similar anatomical structure was previously described in the AME of an agelenid spider by Schröer (1974). Since the detection and analysis of polarized light by agelenid and lycosid AME have also been demonstrated, it is suggested that the analysers of the e‐vector of sky‐polarized light are in the receptor ? cells and that the analysis is a successive process using a twisting of the retina due to the action of two muscles.