The absolute sensitivity of the median and lateral eyes of the scorpion,Androctonus australis L. (Buthidae, Scorpiones)

Abstract

1. The absolute thresholds of the lateral and median eyes of the scorpionAndroctonus australis L. were estimated from averaged electroretinograms (ERG). 2. The lateral eyes of scorpions kept in maintained darkness for 60 days gave measurable ERG responses to light from a uniform hemispherical surround with source radiance of as little as 1.5·10−8 μW·cm−2·sr−1 (for monochromatic light of wavelength 493 nm), during the circadian night phase (Table 1). During the day phase the lateral eyes were less sensitive, by about 0.5 log units (Fig. 4). 3. The median eyes, with a threshold of 1.5·10−7 μW·cm−2·sr−1 during the night phase, were only 1 log unit less sensitive than the lateral eyes at this phase of the circadian cycle (Table 1, Fig. 4). However, the sensitivity of the median eyes during the day phase fell by about 3 log units (Table 1, Fig. 4). 4. The absolute sensitivities of eyes of a given type in the same circadian phase usually varied, among different animals, by less than 1 log unit (Fig. 4). The sensitivity of a given eye in a particular phase, but measured in different circadian periods, was often highly reproducible. 5. The remarkably high sensitivity of the scorpion eyes is discussed with respect to the biology of these nocturnal animals, and compared with that of other eyes.