Fig. 4. Actin filaments are necessary for achieving uniform distribution of pigment. Aggregation of pigment granules was stimulated with 10 µM adrenalin; dispersion with 5 mM caffeine. Control cells (see Sequence 3). Aggregation proceeded to a tight focus within 5 min and dispersion to a uniform distribution within 15 min. Latrunculin-treated cells (see Sequence 4). After normal aggregation, 5 µM latrunculin was added for 15 min before dispersion was stimulated by addition of caffeine. Image acquired 10 min after caffeine addition shows pigment granules accumulated at the cell margin. Some retraction of the cell margin also occurred. Bar, 20 µm.