Fig. 2. Fin nerve stimulation in Sepia officinalis. Still video frames from stimulation of a primary fin nerve branch in one animal, A1 (A1, A2), and one of its secondary branches, A1a (B1, B2), in a different animal. A1 and B1 show the fin immediately prior to stimulation when chromatophores are retracted; A2 and B2 show fin chromatophores expanded during stimulation. Chromatophores expanded in B2 are a subset of those expanded in A2. Although yellow, orange and dark brown chromatophores were all activated, only the latter two colors are visible in the still frames. Scale bars, 5 mm (A1,A2); 6 mm (B1,B2).