140 



THE PHYSIOLOGY OF EARTHWORMS 



The gut is supplied with a plexus which hes within the intestinal 

 wall. The plexus originates from the circum-oesophageal commis- 

 sure where six small nerves leave the ring and send branches along 

 the gut wall. The muscles of the intestinal wall are supplied by 

 nerves arising in the septal plexus of each segment. In the body 



Fig, 42. Diagrams of paired lateral giant axons and the single 

 median giant axon of Lumbricus (from Nicol, 1947). 



wall branches of the motor nerves pass to the circular and longitu- 

 dinal muscle layers, and sensory fibres run from the sense organs 

 on the surface of the body. A sub-epidermal network of nerve 

 fibres has also been described (Smallwood, 1926). 



The relations that exist between the various fibres that comprise 

 the nerve trunks are indicated in Fig. 43. This diagram is based 

 upon anatomical studies, and at the present time little is known of 



