The changes in cell shape accompanying pigment aggregation and dispersion in the hindgut chromatophores of the shrimp Palaemon affinis Heilprin were investigated by scanning electron microscopy. On the dorsal surface of the hindgut, chromatophores with dispersed pigment appear as flattened discs from which radiate short cell extensions. Chromatophores with aggregated pigment appear as raised hemispherical masses which lack cell extensions. These transformations, the result of the movements of pigment granules and cytoplasm, are discussed in relation to the degree of contact between the chromatophores and the surrounding tissues.