168 



THE PHYSIOLOGY OF EARTHWORMS 



Prosser (1935) noted that the segmental pattern of the motor 

 fibres is very similar to that of the sensory fibres, extending to the 

 segments in front of, and behind, the segment of origin, but 

 the effects of stimulation are not so pronounced in the case of the 

 motor axons. The section of one ganglion in the nerve cord delayed 

 the passage of peristaltic waves along the body, and the complete 

 removal of one gangHon stopped peristalsis. Peristalsis only passes 



35 



25 



Time, sec 

 Fig. 55. a single nerve unit of L. terrestris which gave potentials 

 in response to pH 4-0 (©) and pH 3-8 (o), but not to pH 4-2 (d) 

 (from Laverack, 1961a). 



again when one segment is allowed to pull on another, so the 

 peripheral plexus and stretch responses are unable to conduct 

 impulses across more than one segment. 



This has received support from Miller and Ting (1949) who 

 consider the epidermal net to be segmental in arrangement, 

 peristalsis spreading through one segment, but requiring further 

 stimulation of receptors in the succeeding segment before pro- 

 gressing along the body. 



