title: The lateral eyes of the scorpion, Androctonus australis.
abstract: The dioptric apparatus of the lateral eyes of the scorpion, Androctonus australis, consists of a cuticular lens, but lacks a vitreous body. The retina is formed by (1) retinula cells displaying a contiguous network of rhabdoms; (2) arhabdomeric cells bearing a distal dendrite that contacts retinula cells via numerous projections and ends before the rhabdomere of the retinula cells; (3) pigment cells that ensheath retinula and arhabdomeric cells with the exception of the contact regions; and (4) neurosecretory fibres possibly originating in the supraesophageal ganglion. The ratio of the number of retinula to arhabdomeric cells is determined to be close to 2:1 in the three larger anterolateral eyes, in contrast to the median eyes where the ratio is 5:1. The construction of the dioptric apparatus as well as the anatomy of the retina imply that in the lateral eyes of Androctonus australis visual acuity is reduced. A certain degree of spatial discrimination, however, may be retained by the presence of a relatively high number of arhabdomeric cells. It is suggested that the lateral eyes of A. australis mainly function as light detectors, e.g., for Zeitgeber stimuli.
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000648:ultrastructure; D003594:Cytoplasmic Granules / Q000648:ultrastructure; D005123:Eye / Q000648:ultrastructure; D008871:Microvilli / Q000648:ultrastructure; D009490:Neurosecretory Systems / Q000648:ultrastructure; D009940:Organoids / Q000648:ultrastructure; D012160:Retina / Q000648:ultrastructure; D012168:Retinal Pigments; D012605:Scorpions / Q000648:ultrastructure*
chemical_list: D012168:Retinal Pigments