In this the first of 2 papers evidence is presented that the sinus gland, located in the eye stalk of Crustacea, elaborates a secretion or secretions which is blood borne and which controls integumentary chromatophore contraction and expansion. The exptl. evidence that the eye stalks are responsible for the secretion is based upon excision, transplantation, and inj. of extracts, prepared from the eye stalks.