58 THE LEECH. 



2. The vasa deferentia lie to the outer sides of the testes : 

 each is a thick-walled tube, with a small central 

 lumen. 



H. The Nervous System. 



The nerve-chain lies in the ventral sinus, and is readily 

 recognised. Its double character is very obvious in transverse 

 section, and if the section passes through a gangUon the large 

 pyriform nerve-cells can be well seen. Between and below 

 the two halves of the ventral chain lies a slender longitudinal 

 nerve, the intermediary nerve. 



