Fig. 9. (A) Ratio between the sensitivity for 500 nm and 359 nm light determined from intracellular, electrophysiological recordings of a Musca photoreceptor adapted to orange light, the intensity of which is indicated in decadic log units (abscissa; from Vogt et al., 1982). The peak and plateau potential (dotted line, 30 s light adaptation; continuous line, 150 s adaptation) indicate the sensitivity range of the photoreceptor. (B) Pupil absorbance as a function of log adaptation intensity derived from the sensitivity ratio of A together with the relationship between the average sensitivity ratio and the pupil absorbance for photoreceptors with one sensitizing pigment molecule per rhodopsin (Fig. 10, av).