Superimposed images of maxilliped 2 of the crab Carcinus viewed ventrally under bright field and UV illumination. The ventral (outside) cuticle and underlying hypodermis of the exopodite were removed. (A) With the flagellum at its natural resting position (adducted), a strip of bright blue fluorescence on the ventral surface of the joint is almost straight. (B, C, D) As the flagellum is progressively abducted the fluorescent strip becomes progressively bent. (E) Section through the exopodite at the plane indicated by the dashed line in A shows the fluorescence along the bottom surface and wrapping around the ventral and dorsal surfaces. Scale bars A, B, C, D 200 μm, E 100 μm.