On the Existence of Two Types of Chromatic Behaviour in Teleostean Fishes

IT is well known that colour changes of animals may be brought about by (a) direct action of light, heat and other stimuli on the skin chromatophores, as, for example, in the "primary" photic response of Amphibia, and (b) action of stimuli on localized receptors. Co-ordinated responses, i.e. responses of the second type, fall into two categories which offer a striking initial contrast in their time relations. (i) Rapid type, e.g. the responses of the chameleon to local electrical stimulation and of the minnow to light reflected from its surroundings. (ii) Slow type, e.g. the photic responses of Crustacea, Amphibia, Cyclostomes and Elasmobranch fishes.