. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . ^IfiW^ ^ « »*?â Fig. 1. A concentrated melanophore with nucleus (N) in the center. Part of the cell membrane at arrow. The inner cytoplasmic membrane (I) surrounds an inner sack. Magni- fication 3800. Fig. 2. Part of a concentrated melanophore. Nucleus (N), mitochondria (M), pigment granules (P), inner cytoplasmic membrane (I), fibrillar zone (F). Magnification 29,000. They can be simple or double innervated. Tn the former case they only possess concentrating nerve fibres. In the latter case both concentrating
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . ^IfiW^ ^ « »*?â Fig. 1. A concentrated melanophore with nucleus (N) in the center. Part of the cell membrane at arrow. The inner cytoplasmic membrane (I) surrounds an inner sack. Magni- fication 3800. Fig. 2. Part of a concentrated melanophore. Nucleus (N), mitochondria (M), pigment granules (P), inner cytoplasmic membrane (I), fibrillar zone (F). Magnification 29,000. They can be simple or double innervated. Tn the former case they only possess concentrating nerve fibres. In the latter case both concentrating and dispersing nerve fibres are present. The principal hormones acting upon the colour changes are inter- medin, acetylcholine and nor-adrenaline, the former two generally dispersing the pigment granules, the latter concentrating them. Thus the chromatophores are a type of effectors. In this investigation 2-3 cm long females of the com- mon aquarium fish Lebistes reticulatus were used. By placing the fishes on black or white backgrounds during 15 minutes the melanophores in the dermis on the scales were fully dispersed respectively concentrated. Scales from the dorsal and dorso-lateral sides were then quickly removed and immediately fixed at < 4' C during 5 minutes in a solution consisting of g veronal-sodium, g sodium acetate, g sodium chloride, 12 ml HCl A', I g OsO, and distilled water to make 100 ml. This solution is isotonic in relation to the blood of the fishes. After fixation the scales were washed with NaCl A" and dehydrated at +4°C over 70 per cent, 95 per cent and absolute alcohol, 10 minutes in each. The last change of absolute alcohol was carried out at room temperature. The scales were embedded in a mixture of «-butyl-metha- crylate and methyl-methacrylate containing per cent benzoyl-peroxide as a catalyst. Then the mixture was polymerized at 40"C. The sections were made with the Sjostrand Ultramicro- tome. Wit
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