228 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



specialised among the Cyclobranch Docoglossa, and thereby 

 gives evidence of the difficulty of digesting the tough 

 vegetable food: the high development of folds must also 

 enable this region of the gut to act as a strainer, preventing 



the further transport of large fragments into the thin 

 walled regions which follow. The great length and size 

 of the stomach, which is the region where the secretion of 

 the great digestive gland becomes mixed with the food 

 is a further testimony to the slowness and difficulty of the 

 digestive proeess. 



Nervous System and Sense Organs. 



The nervous system of Patella mdgata (fig. 23) may be 

 considered under three headings. 



(a) The Circumcesophageal ring with its cerebral, 

 pleural and pedal ganglia, and the principal nerves thence 

 given oft except — 



(b) The Buccal and Labial nervous systems, connected 

 to the ring at the cerebral ganglia. 



(c) The Visceral Loop and nerves thence given oil, 

 connected to the ring at the pleural ganglia. 



The C i r c u m oe s o p h a g e a 1 R i n g. — This is 

 seen, after exposure of the dorsal surface of the gullet, 

 on pressing apart the gut tissues and body wall in the 

 region of the head and neck. When completely exposed 

 it. is observed to be roughly four-sided, the plane of the 

 quadrilateral sloping downwards and backwards, while 

 its upper and lower sides are curved outwards. The 

 quadrangular form of the ring is due to its having accom- 

 modated itself to the outlines of the buccal mass. Though 

 certain swellings on the ring arc referred to as ganglia, 

 it musi not he supposed that nerve, cells are not found in 

 other parK the concentration of these being by no means 

 complete; The two upper corners of the quadrilateral 



