18 E. NOMURA : 



ing over, the ventral blood-vessel, to which it closely adheres (tig. 

 13). The external tubular portion starts from the anterior corner 

 of the mass and runs postero -laterally with a few convolutions. 

 The external orifice lies rather near the anterior septum of a segment 

 on the ventral setal line. 



b.c pt 







i 



,:_4. 



/ \ 

 / \ 

 / \ 





"m 



m v 



Fig. 13. 



Cross-section through the rcain mass of a nephridium. x 700. v.v — ventral 

 blood-vessel, b.c— blood-corpuscle, pt — peritoneal cell, n.c — nephridial canal. 



5. Nervous system. 



The brain lies on the dorsal side of the buccal cavity between 

 the first and second segment, and is held in its position in the 

 cœlom by the longitudinal muscle fibres of the body wall. When 

 the worm is well narcotised, the brain is almost triangular (fig. 

 14) with a very shallow notch at the posterior apex, but in well 

 contracted specimens it is kidney shaped (fig. 15), with the convex 

 side directed posteriorly. The cross-section of the brain is always 

 elliptical. 



The median prostomial nerve and ganglion are wanting. 



Two lateral prostomial nerves run out pairwise from the 

 anterior corners of the brain into the prostomium, in which they 

 branch and finally enter the body wall. They are very stout and 



