72 



LEECHES 



quantities of both acetylcholine and cholinesterase in the ventral 

 nerve cord of Haemopis. 



The general pattern of lateral nerves is that from each segmental 

 ganglion arise two pairs of nerves. The anterior ones run ventrally 

 at first and then turn outwards following the curvature of the body 

 wall while the posterior pair run to the dorsal half of the body, 

 serving primarily the dorsal body wall, but also sending a branch 

 to the organs in the postero-ventral part of the segment. Each of 



Sensory 

 nerve eel 



Sub-epidermal 

 ring 



ventral 



Gut 



Posterior 

 segmental nerve 



Epider 



egmental 

 anglion 



al muscle 



Fig. 39. Diagram illustrating the lateral segmental nerves and 

 peripheral nerves of Erpohdella. After Bristol, 1898. 



these lateral segmental nerves connects with an inter-muscular 

 nerve ring which circles the body between circular and longitu- 

 dinal muscles. There are two of these in each segment, corre- 

 sponding in position with the anterior and posterior pairs of lateral 

 nerves. There are nerve fibres running longitudinally between the 

 intermuscular rings and others which run to the nervous system 

 lying immediately below the epidermis. Bristol (1898) described 



