Occurrence of Myogenic Hearts in Arthropods

Abstract

A DIRECT demonstration of the myogenic or neurogenic origin of the heartbeat in a given animal requires morphological identification of the structures involved and proof of their pacemaker function by surgical or electrophysiological means. In small animals this is difficult to achieve, and in such cases pharmacological evidence is often used. This indirect line of argument originated with Prosser¹, who showed that the hearts known at the time to be innervated myogenic were slowed by acetylcholine, that purely myogenic hearts were not affected and that neurogenic ones were accelerated. Similarly, Needham² suggested that neurogenic hearts are inhibited by ether while myogenic ones are resistant to it. Although both authors made it clear that such evidence is suggestive rather than conclusive, often in practice no other approach is feasible, and acetylcholine in particular is made to carry the full weight of the argument.