ELECTRORETINOGRAMS AND SPECTRAL SENSITIVITIES OF SOME DIURNAL LIZARDS

Abstract

Electroretinograms (ERG) of Phrynosoma sp., Crotaphytus eollaris and 2 species of Sceloporus have been studied in relation to their form and variability and also to determine spectral sensitivity. All 3 genera have all-cone retinas with yellow oil globules in the cones. The form of these ERG''s varies with the position of the electrode on the retina and with the time after decapitation. Using the ERG with a large p-wave, as in the normal turtle, for measuring spectral sensitivity, and taking the reciprocal of the relative quanta required to evoke a b-wave equal to half that of the response to a standard nearly maximal light stimulus at 590 m[mu] wave length, the spectral sensitivity curve attains a maximum at about 560 m[mu] in all 3 genera. Crotaphytus and Sceloporus show similar curves with a second maximum at 580 m[mu]; both show very low sensitivity to wave lengths below 500 m[mu]. Phrynosoma shows some sensitivity extending to the blue-violet. Individual curves show rather wide variation, but in general they conform to the absorption curve of iodopsin.