THE adaptation of colour in anurans to the background is controlled by hormones. Direct innervation of the melanophores is of little or no importance in controlling the degree of dispersion of the melanin-containing granules within the melanophores1. It is generally agreed that a melanin-dispersing hormone is produced in the pars intermedia of the hypophysis and that this hormone, intermedin, is responsible for the darkening of the skin. It is, however, controversial whether the paling upon transfer to a white, illuminated background is due to the disappearance of intermedin from the blood, or to the secretion of a whitening hormone.