244 Miscellaneous. 



oesophagus and the lingual sac near the point where the salivary 

 ducts open. 



These two ganglia alone constitute the stomato-gastric centre ; 

 above they furnish the salivary and buccal nerves, and below two 

 cords, the stomachal nerves, the stoutest and the longest, which 

 follow the oesophagus to innervate the stomach and intestine. It is 

 curious to remark that there issue from the same centre voluntary 

 nerves appropriated to the mouth, and nerves passing to organs 

 which may probably escape the action of the will, such as the 

 salivary glands, the stomach, and the intestine. 



In a great many cases the two stomachal nerves divide upon the 

 dilatation of the digestive tube preceding the opening of the biliary 

 duct, and, according as it is of greater or less extent, form reticu- 

 lations which may vary infinitely in abundance and arrangement. 

 The Darkles, the Pleurohranchi, the Haliotides, the Tetliydes, and the 

 majority of the Gasteropoda are in this case. But other arrange- 

 ments occur, and the one now to be considered exists in FMline, 

 Bulla, Scajjihander, Aphjsia, &c. 



In these animals, after the lingual bulb, the oesophagus is dilated 

 below into a crop often of vast size, beneath which there is a gizzard 

 furnished with hard pieces destined to triturate the food. This 

 masticatory apparatus is robust and its parts are moved by powerful 

 muscles. Its innervation by a small number of nerves, as in ordi- 

 nary cases, would have been insuflficient, and we note the appear- 

 ance of a series of small ganglionic centres which, if we considered 

 only their development, would be more important than the centres 

 of origin situated, as we have just seen, in the angle formed by the 

 oesophagus and the lingual sac. 



In PhiJine the gizzard is elongated and armed with three lozeiige- 

 shaped hard and resistant pieces. Above it is surroimded by a 

 nervous collar having ganglionic nodules of very variable number 

 and size ; from it issue six constant nerves, often as thick as the 

 stomachal nerves themselves. Those nerves follow the margins of 

 the hard pieces of the armature, and, in passing, innervate the 

 powerful muscles which unite and move them. On arriving at the 

 bottom of the masticator)' apparatus they anastomose and form a 

 new collar as highly developed as the former one ; finally, from 

 this last issue the nerves of the stomach and intestine. To the right 

 the asymmetrical centre emits an anastomotic branch to this nervous 

 apparatus, which is already so rich, and reinforces it still more. 



In Bulla Jiydaiis the three masticatory pieces being rather short 

 than long, the gizzard becomes globular ; but the same muscles, the 

 same superior and inferior collars, and the same ganglia as in Pliiline 

 occur. Only instead of six nerves uniting the two rings there are 

 only three, and the small ganglionic aggregations are larger and 

 better differentiated. 



In Scaphander the masticatory apparatus seems at the first glance 

 to be composed only of two pieces ; but on searching carefully the 

 third very small one is foinid hidden between the two larger-ones; 

 the three nerves uniting the two rings (superior and infeiior) ai'e 



