Specimens of Octopus vulgaris (Cuvier) immersed in cold sea-water (4°C) exhibit a flashing display of brown chromatophores that we call “brown spots”. The spots, which flashed approximately once every three seconds, are distributed over the dorsal skin of the head, mantle and arms and correspond mainly with the distribution of the white spots and white streaks previously described, and appear to act as a screen for the patches composing the white spots. Flashing brown spots could be evoked in animals with the supraoesophageal brain removed but not in animals with local denervation of the skin.
The precise site of action of the cold is unknown but it is proposed that the nerves supplying the brown spot units are normally tonically inhibited and that the cooling process removes this inhibition and allows the spots to flash. They are particularly useful for the in vivo study of the control of chromatophores because they can be reliably activated and isolated from responses of other chromatophores.
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