Transmission Through the Last Abdominal Ganglion of the Dragonfly Nymph, Anax Imperator

Abstract

1. In the last abdominal ganglion of the dragonfly nymph afferent fibres from tactile endings on the paraprocts synapse with large ascending fibres in the ventral nerve cord. The latter run the length of the cord and synapse with efferent fibres in the segmental nerves of the thoracic and abdominal ganglia. The evasion response is mediated by this pathway and can be elicited by electrical stimulation of the nerves from the paraprocts. 2. The synapses between tactile afferents and ascending fibres show delays of 2.0-4.5 msec. and transmit synchronously to frequencies of 50-60/sec. There is no evidence for facilitation at these synapses, but facilitation and/or temporal summation is of importance at the efferent synapses which appear more labile in their properties. 3. Stimulation of the paraproct nerves shows the existence of a reflex connexion between afferents and efferents of the same nerve comparable to that of the vertebrate spinal cord. This provides a preparation for a study of the relationship between sensory and motor neurons in the insect nervous system. 4. Transmission through the last abdominal ganglion and cord is compared with that in the cockroach and locust.