Fig. 1. Photographs of sectioned photoreceptors and lateral screening pigments from four species of fiddler crabs, of genus Uca, as viewed in the microspectrophotometer. In each panel, the elongated rectangular or oval-shaped structures are rhabdoms, sectioned obliquely and viewed laterally, surrounded by droplets or granules of screening pigments. Absorption spectra of these screening pigments are plotted in Fig. 4B. Scale bar, 10 µm (applies to all panels).