:;-J NERYO1 B 81 STEM. 



central gullet ; and the intestine, more or less bent upon itseli 

 ends in a medial. ventral anus. 



One 01- l\vo pairs of salivary glands arc present in the dibran- 

 chiates, but wanting in Nautilus. The liver is always large; and 

 the two hepatic duets are generally glandular. A large :ind 

 sometimes spirally-wound c;ecum is frequent ly developed from 

 the commencement of the intestine, with which the hepatic ducts 

 communicate. The product of the salivary glands is uncolored, 

 limpid and acid, whilst that of the liver and pancreas is also nil- 

 colored and acid, but rarely limpid. 



In the tetrabranchiata and the decapoda the (esophagi! 

 dilated into a crop separated from the stomach by a constrict ion. 

 The ciucnm is small and rounded, and the intestine is twice bent 

 upon itself. The four-lobed loosely racemose liver is lodged in 

 the anterior portion of the perivisceral cavity, and is largely 

 developed. From either side of it spring biliary ducts which 

 open in the large blind-sack ; the pancreas is found at their 

 commencement. 



The Nervous System is mainly identical with that of the 

 eropods. There are the three typical pairs, the cerebral. 

 pedal .'ind visceral ganglia, surrounding the gullet and connected 

 by commissures ; whilst the nerves which supply the buccal 

 mass, the alimentary canal, the heart, the branchia. 1 and the 

 mantle develop additional local ganglia. 



This dibranchiates have the principal ganglia so closely con- 

 neeled that the commissures are not readily perceived. Tin 1 

 optic nerves are well developed. Tin- superior and inferior 

 buccal ganglia have each united in one mass, and the two are 

 united by commissures around the (esophagus. The large nerves 

 of the arms, and those of the funnel or siphon, proceed from the 

 pedal ganglia, which are placed on the posterior side of the 

 U'lillel ; with them :nv connected also the auditory nerves. From 

 the parieto-splanchnic or \ Ueeral ganglia proceed nerves ahm- 

 1 he shell-muscles to the anterior wall of the mantle, where they 

 ent.er the laruv <jtin<ili<i stellftta : these are connected b\- commis- 

 BUres, and send strong cords to the fins. Uraiichcs of the 

 parieto-splanchnic ganglia, following Hie vena-cava, supply the 



