304 CEPHALOPODA. 



the latter has not yet fused with the visceral ganglion (PELSENEER), 

 According to the above author, who is confirmed by BOBRETZKY, 

 the buccal ganglia originate in the same way, becoming abstricted 

 from the cerebral ganglia and shifting forward, but Ussow states that 

 they have a separate origin like the principal ganglia, and unite with 

 these only at a later period. A similar origin is claimed by Ussow 

 for the splanchnic and the stellate ganglia. 



The ganglia can easily be recognised by the fact that, soon after 

 their appearance, a differentiation into an outer cellular layer and 

 a central fibrous mass takes place. 



The connection of the ganglia with the sensory organs and the 

 peripheral parts of the body takes place only at a somewhat later 

 stage. Ussow assumes that the cells of the layer which produced the 

 ganglia lengthen and thus yield the nerve-fibres, as described above 

 (p. 193) for the Gastropoda. 



The above interpretation of the nervous system is not accepted by all 

 anatomists. The anterior part of the sub-oesophageal mass, the brachial 

 ganglion, has been regarded as a part of the cerebral ganglion, which in con- 

 sequence of the great lateral extension of its anterior section, finally stretched 

 below the oesophagus, fused here in the middle line, the anterior part being 

 constricted off and remaining connected only by a commissure with the 

 cerebral ganglion (v. JHERING, GBOBBEN, No. 16). 



The brachial ganglion supplies the arms with nerves ; some of these nerves, 

 however, are said not to arise from the brachial ganglion but to pass into 

 the cerebral ganglion through the anterior commissure (DIETL, No. 10). This- 

 connection and the conditions found in Nautilus have led to the view that 

 the brachial ganglion belongs to the brain. In Nautilus, the majority of 

 the tentacle-nerves spring from the part of the middle oesophageal ring which 

 might be indicated as the pedal ganglion, but some originate above the root& 

 of the optic nerves, and are thus thought to be cerebral in origin. According 

 to this interpretation, the part of the oesophageal mass known as the pedal 

 ganglion would then also have to be reckoned as belonging to the cerebral 

 ganglion, since we cannot claim some of the tentacle-nerves as cerebral 

 nerves and the others as pedal nerves. 



This question is of importance in connection with the interpretation of the 

 arms which, if innervated from the brain, would have to be regarded as 

 cephalic appendages, while, if they derived their nerves from the pedal 

 ganglion, they would have to be considered as parts of the foot. Some of the 

 facts of ontogeny and comparative anatomy have recently been shown to be 

 opposed to the first of these views and to favour the second. According to 

 PELSENEEB, as already mentioned, the brachial ganglion at first forms by 

 abstriction from the pedal ganglion, and is thus not in any way closely 

 connected (as assumed) with the cerebral ganglion. 



Before the brachial ganglion separated from the pedal ganglion, a nerve- 

 strand ran from the anterior part of the (primitive) pedal ganglion to the 



