62 PHYSIOLOGICAL SERIES. 



tin- external renal openings. Just posterior to the subhepatie 

 lair*-, each nerve gives off a branch from its lateral 

 Mir face to the retractor infundibuli, and a little further bark 

 a second branch from its median side to the rectum and 

 ink- 



Dorsal to the external renal openings the two main 

 trunks are united by a plexiform commissure, and from this 

 point continue along the ante ro- lateral margin of the 

 kidneys till they reach the bases of the gills. Hero each 

 forms a ganglion and passes forwards along the gill to its 

 anterior end. Numerous delicate fibres from the plexiform 

 commissure ramify amongst the viscera and establish con- 

 nections with a large splanchnic ganglion situated upon 

 the stomach. The splanchnic ganglion is further connected 

 to the buccal ganglia by an extremely fine pair of nerves 

 that lie upon the walls of the oesophagus. 



From the active predaceous habits of the Dibranch 

 Cephalopods and tbe great concentration of their central 

 nervous system, one may conclude that the latter is a 

 highly-specialised and efficient organ, but as to its 

 actual working little definite is known. It may be 

 -aid, however, that: The cerebral ganglion (in certain 

 cases at any rate, though apparently not in all) exerts a 

 ral inhibitory influence over the rest of the system. 

 In its anterior part is located a centre for the fixation 

 of the arm-suckers, their relaxation depending on another 

 e. -nt re in it< posterior part. Each braebial nerve forms 

 a reflex centre for the general movement- of the arm in 

 which it lies. The plenro-yiaoerml mass, and not as might 

 ! soppotad the stellate ganglion, is the reflex centre for 

 the respiratory movements of the mantle; it is also the 



itrolling centre fur the chromatophon-. 



Tbe action of the heart can take place independently 



of the ee pi ialic central system, although its pulsations are 



ulated by the subocsophageal ma-. 0. C. 1306 E. 



Charon, Ann. Sci. Nat, ser. 5, t. v. 1866, p. 41. 



D. 64. A section of the mantle of a large Cuttle-fish 



officinalis) ihowing <>n< of the pallial nerves with the 

 ganglion stellatum. The branch of the pallial nerve that 



