Fig. 5. Scatter plot showing _max values for middle-wavelength-sensitive (MWS) and long-wavelength-sensitive (LWS) outer segments from individual double cones where both outer segments were measured. The horizontal dashed lines indicate the minimum and maximum _max values predicted for a single LWS opsin with a _max range of 563₁–633₂ nm using Harosi's (Harosi, 1994) model (for model selection criteria, see text). Vertical dotted line predicts the range of _max values for the MWS cones at the short-wavelength range of the data set. Vertical dotted and dashed line predicts the range of _max values based on the long-wavelength range of the data set. All data points fit between these vertical and horizontal limits within the measurement error of the MSP device (±3 nm), except those in the lower range of the LWS data set (see text). Using the lower value of 495₁ nm as the vitamin A₁ observed value, we used Whitmore and Bowmaker's (Whitmore and Bowmaker, 1989) model to calculate that the same opsin would have a _max of 523₂ nm if combined with a vitamin A₂ chromophore. Using the inverse of Whitmore and Bowmaker's (Whitmore and Bowmaker, 1989) model, we estimated that the vitamin A₁-based visual pigment that corresponded to the 548₂ nm MWS cone value at the long-wavelength end of the range would have a _max of 512₁ nm.