Comparison of green rod outer segment sizes in the aquatic and terrestrial phases. The retinae of aquatic (a, c) and terrestrial (b, d) salamanders were double-stained with 4D2 (red), which labels the red rods; and with Blue-N (green), which labels the green rods and blue-sensitive cones ([a, b] low magnification, bar = 40 μm; [c, d] high magnification, bar = 16 μm). Note that the green rod outer segments are larger in size in terrestrial salamanders, than in aquatic salamanders.