Figure 4.

Possible degeneration of blue-sensitive cones during metamorphosis. Flat-mounted retinae from salamanders of the aquatic phase (a–c) and those in the process of metamorphosis (d–f), which had developed lungs but had not lost their gills, were double-labeled with Blue-N (green color), which labels the green rods and blue-sensitive cones (a, d); and UV-N (blue color), which labels the UV-sensitive cones (b, e). (c, f) Superimposed images of (a) and (b), or (d) and (e), respectively. Note that the blue-sensitive cones have substantially thinner outer segments (indicated by white arrows in [d] and [f]) in the metamorphosing salamanders compared to those in the aquatic phase (indicated by red arrows in [a] and [c]) (bar = 16 μm).