XIII] SEPIA 319 



ends in an oval papilla.' A peculiar sac, the ink -sac, the cells 

 lining which secrete the pigment known as Indian ink or Sepia, 

 opens by a long duct on this papilla (Fig. 148). When the Cuttle- 

 fish is alarmed it ejects this ink and darkens the water so much 

 as completely to escape from view. 



The nervous system consists of ganglia even more closely massed 

 than in the case of the snail. The supra-oesophageal ganglia 

 form one rounded mass ; they are produced at the sides into the 

 very much larger optic ganglia which are in close relation to the 

 eyes (Fig. 147). The pedal ganglion is divided into an anterior 

 ganglion called the brachial, and a posterior ganglion sometimes 

 called the infundibular. The brachial ganglion supplies a stout 

 nerve to each arm, and each nerve swells out into a small ganglion 



FIG. 147. Lateral view of the central nervous system of Sepia officinalis. 



Magnified. From Cheron. 



1. Upper buccal ganglion. 2. Nerves connecting buccal ganglion with 



cerebral ganglion. 3. Brachial ganglion. 4. Infundibular ganglion. 

 5. Pleural ganglion. 7. Supra-oesophageal ganglion. 8. Cut 



end of optic nerve. 9. Superior ophthalmic nerve. 10. Pallial nerves. 

 11. Visceral nerve. 12. Anterior nerve to the funnel. 14. Auditory 

 nerve. 15. Inferior ophthalmic nerve. 16. Nerves to the arm. 



The dotted outline represents the buccal mass and the oesophagus. 



just where it enters the arm (Fig. 148). The infundibular ganglion 

 supplies the funnel. 



Posterior to the infundibular ganglion are the two pleural 

 ganglia fused together. These give rise to a visceral loop which 

 supplies the various internal organs and the gills. From the 

 same ganglion two short nerves run to the mantle and terminate 

 in the two large stellate ganglia, which underlie the skin and 

 supply nerves to all the muscles of the mantle (Fig, 148). In all 

 Gastropoda pallial nerves which supply the mantle arise from the 

 pleural ganglia, but in Sepia, owing to the mobility and muscularity 

 of the mantle, the great stellate ganglia are developed in connection 

 with these nerves. The buccal mass is supplied by two ganglia, 



