Scleral differentiation in F4 AE strain, surface fish, and cavefish adults. (a–d) Surface fish (a), F4 AE strain (b, c), and Pachon cavefish (d) double stained for cartilage in blue and bone in red. Arrows. Scleral rims. Arrowheads in (c): Upper and lower scleral ossicles. Percentages under AE in (b) and (c) indicate proportion of adults showing scleral traits (see also e). Scale bar in (a) = 200 μm; magnification is the same in (a–d). (e) Bar graphs showing the percentage of adults with complete scleral ossification (two fully boney ossicles), partial scleral ossification (one or two fully or partly ossified ossicles), or no scleral ossification in surface fish, F4 AE, and cavefish. N is indicated on the bottom of each bar