NATURE OF THE INVERTEBRATE BRAIN. 35 



One of the most striking characteristics of the principal nerve- 

 centres of the cuttle-fish is the fact of the existence of a very large 

 optic ganglion (Fig. 13, 2), in "connection with a well-developed eye, 

 on each side. Each optic lobe, according to Lockhart Clarke, is " as 

 large as the rest of the cephalic ganglia on both sides taken together." 

 From each of these lobes an optic peduncle passes inward to join a 

 supra-oesophageal ganglionic mass, which bears on its surface a large 

 bilobed ganglion (1), thought by Clarke to be homologous with the 

 cerebral lobes of fishes. It is connected, by means of two short cords, 



Fig. 13. Nervous Ststem of the Common Cuttle-fish (Sepia officinalis). 



with a much smaller bilobed ganglion, known as the pharyngeal (7). 

 This double ganglion receives nerves from what are presumed to be 

 the organs of taste and smell, and gives off nerves to the tongue 

 and powerful parrot-like jaws with which the creature is provided. 



The supra-oesophageal mass is connected, by cords at the sides of 

 the oesophagus, with a very large ganglion lying beneath it (4), which 

 is partially divided into an anterior and a posterior division. The 

 anterior division is in relation, by means of large nerves (6), with the 

 feet and tentacles. A commissure also unites it with the pharyngeal 

 ganglion, so that the tentacles and arms are thus able to be brought 



