40 



inaikeJ uorve aiisL'.s from llir piistcridi' bordor ot the 

 ganglion and supplies tlie posterior muscles of tlie 

 odontopliore ; it gives off a branch to the radular sac. 



The Visceral Loo p. — Tracing this loop from 

 the right pleural ganglion, which is easily exposed, wo 

 find that it takes an upward course somewhat toAvards the 

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

 backwards and towards the left, through the salivary 

 glands for a short distance till it reaches the supra- 

 iutestinal ganglion (so-called for phylogenetic reasons, 

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

 forms, ran across above the gut). This gangliou 

 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 connection with the osphradium. From 

 this, and from histological considerations, he seems 

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

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

 osphradium and ctenidial vestige. Ivesuming our con- 

 sideration of the visceral looj) we find that, from the 

 supra-oesophageal ganglion, it goes backwards and 

 towards the right for a short distance and then ruJis into 

 the visceral ganglion. This visceral ganglion gives rise 

 to the following chief nerves :- 



(a) The great visceral nerve which is ricliiy branched 

 and supplies the heart, left kidney, rectum and various 

 viscera. 



{!>) A nerve to the right kidney. 



