NERVOUS SYSTEM 



169 



Summary 



Peristaltic movement in the body w^all of the earthworm is co- 

 ordinated by interaction of central and peripheral nervous activity. 

 Conduction of peristaltic nerves can occur via the ventral nerve 

 cord, but in the case of interruption of this cord can be transmitted 



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200 



100 



^, LIBRARY 



Temperature 



Fig. 56. Graph showing steady rate curve of nervous activity for a 



range of temperatures. The number of impulses rises towards an 



optimum at 13 °C and then falls as the temperature increases 



further (from Laverack, 1961b). 



by tension on the body wall in which stretch receptors are probably 

 present. Rhythms of electrical activity have been described in the 

 ventral nerve cord with a periodicity similar to that of peristalsis. 

 The properties of the components of the reflex arc, sensory, 

 central association and motor, are partly known but much work 



