 It has been argued that octopamine evolved to replace norepinephrine rather than "vice versa"; however, the nervous system of amphioxus (a primitive chordate) has been reported to contain octopamine but not norepinephrine, which presents difficulties for that hypothesis.Early in the twentieth century Walter Cannon, who had popularized the idea of a sympathoadrenal system preparing the body for fight and flight, and his colleague Arturo Rosenblueth developed a theory of two "sympathins", "sympathin E" (excitatory) and "sympathin I" (inhibitory), responsible for these actions.The Belgian pharmacologist Zénon Bacq as well as Canadian and US-American pharmacologists between 1934 and 1938 suggested that noradrenaline might be a sympathetic transmitter.