Anatomy and Affinities of Hypsobia nosophora. 407 



septum [cf. Robson (12)], which, as in tlie Paludesti-inidre, 

 passes between the pedal ganglia and the cerebro-pleural 

 complex. 



V. The Nervous System. (Figs. 4 & 5.) 

 (a) Sense-organs. 



1. Osjyhradium. — This is a small rod-shaped organ lying, 

 as usual, on the left-hand side of the gill. It is 

 innervated by a conspicuous nerve rising from the 

 supra-intestinal ganglion. 



Fiff. 4. 



H. nosophora. Central nervous system (anterior aspect). 



/c=left cerebral ganp^lion; //;/=left pleural gang-lion; ji) = pedal ganglion ; 

 ;Y)/=rigbt pleural ganglion; pj) = (sc.) parapodial and propodial 

 ganglia; sr = supraintestinal ganglion; s&«"=subintestinal gan- 

 gliou ; o = ospbradial nerve ; rc = visceral commissure. 



