Giant Fibre and Small Fibre Pathways Involved in the Evasive Response of the Cockroach, Periplaneta Americana

Giant fibres were found not to activate leg motoneurones during evasion. A pathway of small axons having a conduction velocity of 1 ·5 −3 ·5 m./sec. was found to govern leg activation during escape. This pathway remains functional after giant-fibre degeneration after the giant axons have been severed from their somata. Movements of the antennae were found to be activated by the giant fibres simultaneously or slightly earlier than movements of the legs. It is suggested that a general alarm system is activated by the giant fibres concomitantly with activation of the leg motoneurones by a slower conducting pathway.