34 W. BALDWIN SPENCER. 



arises which runs downwards close to the oesophagus^ and 

 supplies the muscles lying just behind the oesophagus, and 

 those which are concerned with the posterior wall of the 

 pharynx. 



(3) Above the last and just behind the first mentioned 

 arises a nerve on each side. This runs forwards through the 

 head region, keeping close to the ducts from the hook-glands 

 until it reaches the large sensory papillae on which open the 

 ducts of the glands (fig. 49). This nerve is a very distinct 

 one, and from it probably, though I have not been able to 

 definitely follow their course, arise branches to the smaller 

 sensory papillae on the dorsal surface of the head (fig. 34). 

 The sole function of this nerve is that of supplying sense- 

 organs, as, though it runs through the head region where 

 muscles are largely developed, it gives off no branches to 

 these. 



The sensory papillae, and amongst these the '^Tastpapillen" 

 of Leuckart, are hence innervated from a post-oesophageal 

 nerve mass. 



(4) Just behind the last, and slightly ventral to them, a 

 nerve passes off which runs forward to the level of the oeso- 

 phagus, and then curves backwards, supplying the muscles at 

 the side of the anterior and middle part of the body. 



(5) From about the middle of the length of the nerve mass, 

 and dorsal of the last mentioned, arises on either side a nerve 

 which runs forwards and slightly upwards, and after passing 

 to about the level of the anterior end of the mid -gut divides 

 into two. Each division then passes in amongst the muscles 

 of the head region, and its course becomes very difi&cult to 

 follow, but after repeated examination of sections cut in 

 various directions, I have been able to trace it into distinct 

 connection with a curious structure which lies in the basal 

 part of each hook. The appearance of this is shown in fig. 

 33. Between the extensor and retractor muscles of the hook, 

 each of which is attached to the internal surface of the basal 

 joint {B. Hk.), runs a fibrous structure which is in direct con- 

 tinuation with the nerve now under consideration. The latter 



