No. 2. ] THE MORPHOLOGY OF DERO VAGA. I55 
lateral walls of the proboscis. The third nerve passes down- 
ward and slightly forward, and lies close to the anterior wall of 
the buccal cavity. From the distribution of the first three 
nerves it seems probable that some fibres at least in each of 
them are sensory. The fourth nerve (z.4) is situated at some 
distance from the third, but I have been able to trace ganglion 
cells from the dorsal ganglion as far down the commissure as 
the place of origin of this nerve. 
(c) The Sympathetic System. 
Two systems of visceral nerves have been described under 
the name “sympathetic nerve.” Leydig! distinguished the two 
by the names “sympathetic” and “vagus.” The system covering 
the pharynx he called the vagus nerve, and applied the term 
“sympathetic” to the system distributed over the intestine. 
Other writers speak of his vagus as the ‘“‘ sympathetic of the 
head” or simply as “‘ sympathetic nerve.” 
The sympathetic in this latter sense has been described in 
many annelids, both marine and fresh-water. Beddard says:? 
‘«‘T have never found it to be wanting in any earthworm where 
I have looked for it.” 
Vejdovsky has described this system in Chaetogastridae and 
also mentions having found a ganglion on the posterior part of 
the pharynx of a young specimen of Wazs elinguis. So far as 
I know, this is the extent of the work on this system in the 
Naidomorpha. 
The pharynx of Devo vaga occupies the first four setigerous 
segments, and is composed of two very unlike regions. The 
dividing line is the boundary between the second and third 
setigerous segments. The lumen of the anterior half is divided 
into a dorsal and a ventral part by an infolding of the wall on 
either side (Pl X4IT, Pig:\5). 
The main branches (Pl. XIII, Fig. 5, 2.5.2.) of the sympa- 
thetic (vagus of Leydig) nerve lie in the groove between these 
two divisions and extend back to the ganglia (Pl. XIII, Fig. 4, 
1 F. Leydig, Ueber den Bau des thier. Korpers, Tiibingen, 1864. 
2 Beddard, /.c., p. 20. ; 
