120 THE SNAIL 



From their under or ventral surface a pair of buc- 

 cal nerves run forwards alongside the oesophagus, 

 and end in a pair of small buccal ganglia, which lie 

 at the outer sides of the salivary ducts close to their 

 openings into the buccal mass. The buccal ganglia 

 are united by a transverse commissure, and from 

 them nerves arise supplying the buccal mass. 



From the posterior and outer border of each 

 supra-cesophageal ganglion two stout connectives 

 pass downwards and slightly backwards to the sub- 

 (Bsophageal ganglia. Between these two on each 

 side is the slender auditory nerve. 



2. The sub-oesophageal ganglia are a number of closely 



approximated ganglionic masses, the boundaries of 

 which are difficult to determine. The anterior aorta 

 runs through the centre of the mass, ^^airking the 

 division between the antero-inferior portion, or pedal 

 ganglia, and the postero-superior portion, or viscero- 

 pleural ganglia. 



The pedal ganglia are a pair of closely apposed 

 masses, from which a number of large nerves 

 pass to the foot. 

 b. The viscero-pleural ganglia consist of at least two 

 pairs of gangHonic masses, closely apposed to each 

 other and to the pedal ganglia. From them large 

 nerves pass outwards to the viscera and to the 

 body-wall. 



3. The structure of the ganglia. 



Bemove one of the ganglia ; place it in 1 per cent, acetic 

 acid for a short time to soften the connective tissue, and then 

 tease it on a slide in glycerine. Cover ; and examine it with 

 low and high powers. 



The nerve-cells are large granular cells with very 

 large and distinctly reticulate nuclei, and with long 

 branching processes by which they are connected 

 with one another and with the nerve-fibres. 



