Edible Snail. 53 



either side ; the muscular envelope which was continuous with 

 this part of the integument, and formed the floor of the mantle 

 cavity on the one hand^ and a roof over many of the viscera not 

 already specified on the other, has been removed, as have also 

 all the viscera unconnected with the mantle, except the nerve 

 system and the buccal mass. A black bristle has been passed 

 through the nerve collar, between the supra-oesophageal cerebroid 

 ganglia and the commencement of the digestive tube ; and another 

 has been inserted between the stomato-gastric ganglion of the right 

 side, and the back part of the buccal mass. A stout nerve passes 

 from either side of the supra-oesophageal mass to the superior 

 or eye-bearing tentacle, indicating thus by its distribution the 

 sensory character of the nerve centre whence it arises. The in- 

 ferior tentacles are supplied from the same source, as are also the 

 rudimentary ' organs of Semper/ and the upper lip. A long and 

 delicate commissural cord is seen to connect the cerebroid mass 

 with the stomato-gastric ganglion, which is placed in the I'e-entering 

 angle between the oesophagus and the retracted buccal mass. A 

 much stouter and double commissural cord is seen passing down- 

 wards, from the supra-oesophageal mass on the right side. By one 

 of its strands, the shorter and the more posteriorly placed of the 

 two, it connects the upper or parieto-splanchnic portion of the 

 sub -oesophageal mass with the supra-oesophageal of its own side ; 

 and by its longer and more anteriorly placed, it comes into a 

 similar relation with the lower or pedal portion of that part of 

 the nerve collar. From the upper part of the sub-oesophageal 

 mass, three nerves pass off to the parietes, as opposed to the foot, 

 two on the right side, and one on the left. Certain other nerves 

 which supply the columellar retractor muscles, as also the great 

 visceral nerve, which has been removed together with the aorta, 

 which it accompanied, had a similar origin. Immediately below 

 the origin of these nerves, the small otic vesicles may be seen 

 situated at the upper and posterior aspect of the pedal mass, which 

 is so closely connected with the parieto-splanchnic portion of the 

 sub-oesophageal mass in the Helicidae, as to be differentiated from 

 it mainly by the position of these vesicles externally, by the orifice 

 through which the cephalic aorta passes mesially, and by the 

 Origin of the nerves passing off" to the locomotor-disc or ' foot* 

 inferiorly. 



