The Mechanism of Locomotion in the Leech ( Hirudo Medicinalis Ray)

Abstract

Considerable uncertainty still exists concerning the nature of the mechanism which maintains the normal locomotory rhythm of terrestrial animals. Two types of theory have been advanced: (i) That the rhythm is determined by the existence of a closed chain of peripheral reflexes, each phase of a complete locomotory cycle setting up automatically the particular pattern of peripheral stimulation requisite for the elicitation of the succeeding phase in the cycle, (ii) That the rhythm is, fundamentally, a property of the central nervous system which is, however, susceptible to modification or extinction by peripheral stimulation.