148 



COMPARATIVE ANATOMY 



CHAP. 



(1) Two cerebro-brachial ; (2) two cerebro-infunclibular ; (3)' two 

 cerebropleural ; (4) two brachio-infundibular ; (5) two pleuro-infundi- 

 bular ; (6) two pleurobrachial connectives. The close proximity of 

 the]' visceral ganglia to the peri-oesophageal mass makes it impossible 

 any longer to distinguish the visceral connectives. 



The cerebral ganglia give rise to the two optic nerves (which soon swell into the 



enormous optic ganglia at 

 the bases of the eyes), the 

 auditory nerves, the olfac- 

 tory nerves (which for a 

 certain distance fuse with 

 the optic nerves), and the 

 connectives of the buccal 

 ganglia. 



The brachial ganglia 

 send off separate nerves to 

 the arms, which nerves are 

 connected by a hoop-like 

 commissure round the base 

 of the circle of arms. Run- 

 ning through the arms, the 

 nerves swell into succes- 

 sive ganglia which corre- 

 spond with the transverse 

 rows of acetabula. 



The separation of the 

 pedal ganglion into a bra- 

 chial and an infundibular 

 ganglion can be proved on- 

 togenetically and anatomi- 

 cally. There is no such 

 separation in the male 

 Nautilus, the brachial and 

 infundibular nerves spring- 

 ing from one and the same 

 ganglion. In Argonauta 

 (Fig. 128, F) the separation 

 is not externally visible, 

 but in Octopus (E) we see 

 the first traces of it ; in 

 Si'ina (D), LoUrjo (C), and 

 Sepiola (B), it becomes 

 more and more evident, till 

 finally in Ommatostrcphes 



(A) the distinct brachial ganglion has moved away from the infundibular ganglion, 



with which it is joined by a slender externally visible connective. 



In this same series, the separation of the so-called upper buccal ganglion from 



the cerebral ganglion also takes place, the buccal remaining united to the brachial 



ganglion by the brachiobuccal connective. 



The parietal ganglia give rise to the two large pallial nerves. Each of these runs 



backward and upward, and enters the stellate ganglion on the inner surface of the 



iO 



FIG. 128. Central nervous system of various Dibranchia, 

 from the-right side. All the figures after Pelseneer. A, Ommato- 

 strephes ; B, Sepiola ; C, Loligo ; D, Sepia ; E, Octopus ; F, Argo- 

 nauta. 1, Cerebral ; 2, pedal ; 3, visceral ; 4, brachial ; 5, upper 

 buccal ganglion ; 6, infundibular nerve; 7, visceral nerve; 8, optic 

 nerve cut through; 9, pallial nerve; 10, brachial nerves; and in 

 Fig. B the pharynx ()>h), and oesophagus (u) are drawn in black. 



