That the pituitary is the source of humoral agents that effect the pigmentation of vertebrates, has been known since the classic experiments of Smith 1 and Allen2 who revealed that tadpoles deprived of their hypophysis are much more lightly colored than are their intact counterparts. We now refer to these agents as melanotropins, although, in many ways, this term is misleading. Because the principal source of melanotropins is the intermediate lobe of the pituitary, it was designated "intermedin" by Zondek and Krohn' who reported on the ability of this hormone to stimulate red pigmentation in a European minnow. Later, in keeping with the principle that hormones be named for their function rather than their source, melanocyte-stimulating hormone (MSH) emerged as the preferred designation for the hormone.4 Indeed, a principal function of MSH is that it stimulates melanophores (melanocytes); however, the fact that this melanotropin also controls the bright-colored nonmelanin-containing cells of lower vertebrates has been recognized from the very first. 5 In view of the diversity of pigmentation among vertebrates and the profound and variable color changes exhibited by lower vertebrates in response to this hormone, MSH must truly be viewed as a chromatotropin.