204 BULLETIN OF THE 



arise by cell proliferation from the dorsal margin of the ventral wall of 

 the head or trunk region, above that which I have called the pleural 

 groove. Further, that the right visceral (or supra-intestinal) ganglion 

 is connected by a nerve fibre to the olfactory ganglion under the gill 

 cavity. Farther back than the visceral ganglia he finds a median pro- 

 liferation of cells lying at the ventral margin of the gill cavity, from 

 which the abdominal ganglia arise. He asserts that there are two ab- 

 dominal ganglia, — one connected with the supra-intestinal ganglion, 

 the other with the sub-intestinal ganglion. 



In Limax maximus the visceral ganglia and the abdominal ganglion 

 arise by the same method as that described by Sarasin ; but the former 

 are produced from the lateral walls of the head region, above the pleural 

 groove, one on each side of the body. The right ganglion in later stages 

 is more dorsal than the left. It appears to be formed in part from the 

 inner wall of the respiratory cavity, to which it remains connected by a 

 nerve. It is in this region that is developed an organ which I believe 

 to be the olfactory organ of Lacaze-Duthiers. 



There is only one abdominal ganglion ; this takes its origin a little to 

 the left of the median line of the body, from the anterior margin of the 

 body wall immediately above the pleural groove. 



Sarasin ('82) is the only author who gives attention to the origin of 

 the buccal ganglia. He describes them as arising in exactly the same 

 manner, and in the same situation in relation to the walls of the radula 

 sac and the oesophagus, that they do in the case of Limax maximus. 



Cambridge, November, 1889. 



