THE CEPHALOPODA 



315 



are united by a thin supra -oesophageal commissure in the adult. 

 The pedal centres proper supply nerves chiefly to the funnel, and 

 thus correspond to the dorsal moieties of the pedal cords of 

 Rhipidoglossa which innervate the epipodium ; but they also send 

 fibres to the brachial nerves, and therefore, in conjunction with 

 the brachial ganglia, control the locomotory functions. 



The pleural centres lie on the sides of the posterior part of 

 the sub-oesophageal mass ; they are but little differentiated and 

 scarcely visible externally, and they give off the two great pallial 

 nerves (Fig. 281, pi). The visceral 

 centres are situated on the ventral 

 side of the mass, and give off the 

 large visceral nerves, which arise 

 separately in Spirula and the 

 Octopoda, but are more or less 

 fused at their origin in Ommato- 

 strephes, Sepia, etc. The pallial 

 or "stellate" ganglia (Fig. 281, 

 gang.stdl) are secondary centres 

 on the course of the pallial nerves, 

 and are situated on the internal 

 wall of the mantle near its an- 

 terior or dorsal border. These 

 ganglia are connected by a trans- 

 verse supra-oesophageal commis- 

 sure, which is slender and is 

 formed by the union of the two 

 nerves of the pallial siphon in 

 Spirula, is larger in sundry other 

 Oigopsida (Ommatostrephes, Ony- 

 choteuthis, Enoploteutliis, Gonatus, 

 Veranya, Thysanoteuthis), is re- 

 duced in Loliyo, and is absent in 

 the adult Sepiola. This commis- 

 sure, together with the two fused 



G ... . Lateral view of the nervous centres and 



nerves OI the pallial Siphon Ol nerves of the right side of Octopus vulgaris. 



Spirula, represents the two primi- 

 tive pallial nerves, and is the 



homologue Of the pallial COrds, nerve ; ped, pedal ganglion ; pi, pleural 

 ., j i r -, , ganglion ; t'tsc, visceral ganglion. (After Lan- 



united by a commissure dorsad kester.) 



of the intestine, of Amphineura ; 



whereas the large pallial nerves of the Dibranchia are neogenetic 



structures, evoked by the great development of the mantle 



borders, which are reflected over and finally enclose the shell, 



and give rise to the fins, etc. In some cases the visceral nerves 



are also united by a commissure in the form of a transverse 



FIG. 281. 



