Fig. 2. Frequency distribution for all of the single-cone photoreceptor 
max values sampled from all 22 species. Five classes of single-cone photoreceptors were categorized based upon the observed frequency distribution.
Fig. 2. Frequency distribution for all of the single-cone photoreceptor max values sampled from all 22 species. Five classes of single-cone photoreceptors were categorized based upon the observed frequency distribution.