40 



marked nerve arises iidin the pusteiior Ixudei of tJie 

 gaugliou and snpplies tlie pusteiior niuseles of tlie 

 odontopliore ; it gives uli a brancli to the radular sac. 



T li e y i s c e r a 1 Loo p. — Tracing this h)o}) from 

 the right pleural ganglion, which is easily exposed, we 

 find that it takes an uj)ward course somewhat towards the 

 left, and soon enters the visceral regitni, wherein it travels 

 hackwards and towards the left, through the salivary 

 glands for a short distance till it reaches the supra- 

 intestinal ganglion (so-called for phylogenetic reasons, 

 because it is on the connective which, in pre-Docoglossan 

 forms, ran across above the gut). This ganglion 

 varies very much in size and distinctness, but from it is 

 always given off a long and slender connective which runs 

 across to the left side above the crop and terminates in 

 a ganglion just beneath the left osphradium. This 

 osphradial ganglion supplies the sense organs near it, and 

 Bouvier has also found a slender nerve arising from it 

 which loses itself near the anterior wall of the peri- 

 cardium. This, he says, is the vestigial ctenidial nerve, 

 and it has no connectum with the osphradium. From 

 this, and from histidogical considerations, he seems 

 disjMJsed to argue that the osphradium, so-called, is 

 entirely such, and not, as is commonly believed, both 

 osphradium and ctenidial vestige. liesuming our con- 

 sideration of the visceral loop we hnd that, from the 

 supra-cesophageal ganglion, it goes backwards and 

 towards the right for a short distance and then runs into 

 the visceral ganglion. This visceral ganglion giA-es rise 

 to the following chief nerves : 



(rt) The great visceral nerve Mliich is ricbiy branched 

 and supplies the heart, left kidney, rectum and various 

 viscera. 



(h) A nerve to the right kidney. 



