154 THE PHYSIOLOGY OF EARTHWORMS 



junction. It becomes less easy to exhaust the rear segments after 

 removal of the sub-oesophageal ganglion or severance of the ventral 

 nerve cord in front of the cHtellum. If the ventral nerve cord is cut 

 behind the clitellum it becomes less easy to stimulate all the 

 segments. 



Control of Gut Movements 



The body of the earthworm may for simplicity be considered as a 

 tube within a tube. And in some ways the physiology of each of the 

 tubes is similar. Both show peristaltic movements, and both appear 

 to be under nervous and humoral control. 



The intestinal tract of Lumbricus receives a double set of nerves, 

 analogous to those of the vertebrate gut. One set of nerves arises 

 from the circum-oesophageal nerve ring, and forms a plexus that 

 runs between the mucus membranes and the muscle layers of the 

 intestine. The second set of nerves comes from the ventral nerve 

 cord running up via the septum to the gut. 



Wu (1939a) considered these two nerve supplies to be antago- 

 nistic in function. Excitation of those arising in the ventral nerve 

 cord led to a decrease of the motility of the gut wall, whilst 

 stimulation of the nerves from the oesophageal commissures is 

 excitatory to the gut. Millott (1943 a, b) questions this simplified 

 view, considering that the septal nerves contain both excitor and 

 inhibitor fibres, and that the function of the oesophageal nerves is 

 not clear. Millott (1944) also noted that stimulation of the ventral 

 nerve cord not only affected the tone of the gut but also increased 

 the secretion of protease enzyme within the gut lumen. He 

 adduced evidence that the nervous pathway involved in this system 

 passes from the ventral nerve cord to the peritoneum applied to the 

 body wall inner surface. The nervous pathways then ran through 

 the ventral part of the intersegmental septum and thence to the 

 plexus of the gut. Quite why such secretory-stimulating nerves 

 should come via the body wall is not apparent, especially as they 

 seem to be located more on the internal surface of the muscle 

 layers than deeper within the body wall. 



Pharmacological evidence indicates that despite the confusion 

 regarding innervation the system is undoubtedly a double one. 

 The muscles of the intestine of earthworms contracts under the 

 influence of acetylchoHne (Wu, 1939; Millott, 1943 a, b; Ambache 



