372 



Memoirs of the Indian Museum. 



[Voi,. V, 



The rectum as usual passes through the ventricle in the pericardial chamber over 

 the posterior adductor muscle to end in the anus. 



The liver surrounds the stomach. Ventrally it extends beyond the first loop of 

 the intestine to the dorsal aspect of the pyloric coecum. Anteriorly it extends to the 

 close coils of the intestine. 



VII. Nervous System. 



The cerebral ganglia are fusiform in shape, and are placed obliquely on the side 

 of the gullet, the posterior lower end lying just behind the groove at the base of the 

 foot. Each ganglion lies just above the junction of the inner and outer lamellae of 

 the outer and inner labial palps. 



The cerebral ganglia are joined to one another by an intercerebral connective lying 

 transversely over the oesophagus as usual. 



The cerebro-pedal commissure passes downwards just behind the junction of the 

 foot with the visceral mass and joins the pedal ganglion of the same side. The 

 direction of the cord varies according to the condition of the foot ; when the foot is 

 fully extended, the cord is directed downwards and forwards from the cerebral gang- 

 lion, but it is directed downwards and backwards when the foot is retracted. 



The cerebro-visceral commissure passes backwards lying just above the attachment 

 of the inner and outer lamellae of the outer and inner labial palps. As it passes 

 backwards it penetrates the wall of the visceral mass obliquely and comes to lie on 

 the inner side of the wall at the anterior end of the gills. It runs backwards, 

 lying along the attachment of the gills, and is gradually displaced upwards till it 

 comes to lie on the inner side of the kidney between it and the wall of the visceral 

 mass beyond the posterior loop of the intestine. It then comes to lie beneath the 

 kidney towards its outer side. In its further course it is gradually displaced towards 

 the inner side and lies between the kidney and the posterior retractor muscle of the 

 foot. Lastly the two cords lie side by side till they end in the visceral ganglia. 



The pedal ganglia are closely applied to one another, lying in the middle line 

 towards the dorsal aspect of the foot at its base a little in front of the mouth. When 

 the foot is retracted, the ganglia recede backwards and come to lie considerably 

 behind the cerebral ganglia. Three nerves can be followed from each pedal ganglion : 



(i) Passes horizontally forwards and divides into two branches which can be 

 traced beyond the middle of the foot. 



(2) Passes obliquely forwards and downwards to the middle of the foot. 



(3) Passes downwards and a little forwards towards the ventral aspect of the foot. 



The visceral ganglia are closely applied to one another and are placed between 

 the two posterior retractors of the foot and beneath the rectum. The ganglia are 

 displaced forwards from the posterior adductor muscles. The two posterior palliai 

 nerves can be traced to the under surf ace of these muscles. 



VIII. Vascular System. 



The pericardial chamber is elongated, and is much narrowed down and compressed 

 posteriorly over the rectum. 



