NERVOUS SYSTEM. INVERTEBRATA. 51 



particularly large. A pair of long slender connectives ari-r 

 from a lobe (fig. 16, PL.L.) on the posterior surface of < i arli 

 cerebral ganglion and accompany the alimentary canal ; 

 near the visceral mass each crosses to the opposite, side of 

 the body the left below the gut and the right above, 

 and upon reaching the visceral mass is joined by the 

 above-mentioned pedo-visceral connective, and swells to 

 form a small visceral ganglion upon the surface; of the 

 gastric gland. These two visceral ganglia represent the 



Fig. 16. 



n n 



O.N. 



PLV.C. '- 

 Cerebral Ganglia of Carinaria mediterranea. 



C.P.C. Cerebro-pedal connective. O.N. Optic nerve. PL.L. Pleura! lobe. 

 PL.V.C. Pleuro-visceral connective. 



supra- and subintestinal of a Prosobranch ; each is united 

 by a delicate filament to a large abdominal ganglion 

 situated upon the gastric gland midway between the two. 

 The gill is innervated from the supra-intestinal ganglion. 



Ganglia comparable to the pleural of other Gasteropoda 

 are not present as independent centres ; they are probably 

 fused with the cerebral ganglia, forming the lobes from 

 which the visceral loop arises. 



Pelseneer, C. R. Acad. Sci., t. cxiv. 1892, p. 775. 



\ 



D. 50. Two specimens of the nervous system of a Roman Snail 

 (Helix pomatioi), shown respectively in situ from the left 

 side, and isolated. 



The central system is much, concentrated. It consists of 

 two main ganglionic masses (i.) a paired oblong cerebral 

 ganglion, united by two connectives on either side of the 



E2 



