ANATOMY AND PHYSIOLOGY OF A SNAIL. 



37 



recoils from strong smelling liquids such as turpentine, which it 

 invariably does when one or both are present. In Limnaa stag- 

 nalis and Planorbis the infra-cesophageal ganglia are orange or 

 red-coloured, and very pretty indeed. The nervous system of 

 Limncea stagnalis well dissected out is the prettiest dissection I 



Fig. 10. a, Nervous system of Haliotis (diagrammatic after Sprengel) ; Cg, cir- 

 cum-cesophageal mass ; Pg, pedal ganglion ; P/g, pleural ganglion (commissural 

 ganglion) ; Ag, abdominal ganglia ; O and O" olfactory organs ; Pe, pedal cord ; 

 6" and S' lateral nerves ; Br, gills ; b, nervous system of Limncea , (after Lacaze- 

 Duthiers). 



have ever seen. The circum-oesophageal mass in the large 

 Tritons is almost cartilaginous to the touch. 



THE OLFACTORY ORGANS. The sense of smell may exist in the 

 supra-pedal gland, the dorsal tentacles, or in the lobate processes 

 around the mouth. An osphradium is to be found in Limncea, 

 Planorbis, and Physa consisting of ganglion cells in relation with a 

 depression in the mantle-chamber above and behind the pulmonary 



