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Department of Biology, University of California, Los Angeles, California 90024, U.S.A.

M.R.C. Vision Unit, University of Sussex, Falmer, Brighton BN1 9QG

1. A dual system of visual pigments having absorbance maxima in the green and blue respectively has been found in the retinas of geckos both by single cell microspectrophotometry and by the method of extraction. Microspectrophotometry has shown the system to be present in four species of geckos representing four genera. Along with previous work with extracts (Crescitelli, 1972) this indicates a fundamental property in this family of lizards. No other photopigments have been detected.

2. For Gekko gekko, the species most intensively studied, the two pigments have absorbance maxima at 521 and 467 nm respectively. Both are based on vitamin A₁ and both are characterized by absorbance spectra that nearly conform to the Dartnall nomogram.

3. In situ, the 521-pigment is not temperature-sensitive, and has virtually the same absorbance spectrum at 23° C as at 5° C. On extraction into digitonin solution, however, the absorbance spectrum of the pigment becomes temperature-dependent and, though identical when measured at low temperature (2-5° C) with the constant in situ curve, is displaced to shorter wave-lengths at higher temperatures (10-25° C). Thus the extract spectrum is relevant to the in situ spectrum only at low temperature (and in the presence of chloride ions).

4. Unlike the rhodopsins of several vertebrates, the gecko 521-pigment displays no evidence of a meta-III stage in the sequence of products following photic bleaching, even at low temperatures. This is true for the pigment in situ as well as in the extracted condition.