ABSTRACT
Nerve muscle preparations of the segmental nerves and associated muscles have been made using a nereid polychaete, Neanthes brandti (Malmgren).
Two kinds of response, differing in threshold and latency, were found. The ‘fast’ response is large at the first shock and (at frequencies above 1/sec.) decreases thereafter. The ‘slow’ response is small but facilitates with repetition at frequencies above 10/sec. Facilitation reaches a maximum after 3 or 4 shocks.
Isolated parapodia show several distinct reflex movements to mechanical and chemical stimuli. These must involve motor neurons in the parapodial ganglion.
Stimulation of the segmental nerves of the leech, Hirudo, evokes facilitating muscle potentials resembling in most details those of the ‘slow’system in Neanthes.
The ‘fast’ and ‘slow’ responses are discussed in comparison with other invertebrate systems, especially those of arthropods. The ‘slow’ responses in annelids show less facilitation. The ‘fast’ responses of polychaetes fatigue quickly and are probably useful only in ‘startle’ responses.
