230 PROCEEDINGS OP THE ACADEMY OP [1883. 



(g. cerebroides), and five inferior (g. sous-oesophagiens). Of these 

 latter, two lie laterally {g. superieurs), and two lie below the 

 oesophagus (g. antero-inferieurs.) The fifth is an odd one, and is 

 placed between the lateral and the inferior ganglion of the left 

 side, and was called the supplementary ganglion {g. supplemen- 

 taire). 



The lateral ganglia are now generally known as the pleural or 

 visceral ganglia, and the inferior the pedal ganglia. In A. lacus- 

 tris the supplementary ganglion lies between the visceral and 

 pedal ganglion of the right side. The reason of this difference of 

 position of the supplementary ganglion is probably that in A. 

 fiuviatilia the genitals, wliich are in part supplied by tliis gan- 

 glion, lie on the left side; while in the other form, where the 

 genitals are on the right side, tlie supplementary ganglion is also 

 on that side. 



J'urther, Moquin-Tandon ' speaks of two small ganglia, which 

 are joined hj connectives'^ v^'ith. the cerebral ganglia, and which 

 he calls the buccal ganglia. 



According to Moquin-Tandon, then, the nervous system of 

 Ancylus consists of nine ganglia. Tliere exist, however, other 

 ganglia, which Moquin-Tandon did not find. Two of these lie in 

 the tissue of the left mantle of A. fluviatilis and in the right of 

 A. lacustris. The other two form a pair, and lie in the cephalic 

 portion, at the base of the tentacles, near the position of the eyes. 



First we will consider the two ganglia that are situated in the 

 substance of the mantle. They lie in the upper pai't of the same 

 between one of the windings of the kidney and the musculus 

 cochlearis. These two ganglia are best seen in a horizontal section. 

 They are very small, so that it would be hardly possible to 

 demonstrate their existence by dissection. They are connected 

 by a bundle of nerve-fibres ; besides this, there comes a bundle of 

 nerve-fibres from the body to the posterior of these two ganglia. 

 Although I was unable to demonstrate the connection of this 



^ liecher. anat. physiol. s. I'Aucyle, etc., p. 129, et seq. 



' I use the expression ^^ connective,^ ^ employed by Lacaze-Duthiers (Du 

 Systeme Nerveux d. Mollus. gastrop. pulmon. aquat. etc. Archiv. d. 

 Zoologie Exp. et Gen., Tome 1, 1B72), for those bundles of nerve-fibres 

 which join ganglia of the same side, in opposition to the term '^ commis- 

 sure,^^ which isouly emjiloyed to denote tliose nerve-flbres that join ganglia 

 of opposite sides. 



