CEPHALOPODA, 



61o 



like tlie flying fish for a short distance through the air. This is 

 the highest act of locomotion, the nearest approach to flight, which 

 any of the molluscous animals have presented. 



We find associated with the varied and active powers of loco- 

 motion just described, visual organs of large size and singular com- 

 plexity of structure ; the whole surface of the body is highly 

 sensitive; and there is a concomitant development of the nervous 

 centres, which exhibit the highest conditions of this system in the 

 Invertebrate series of animals.* 



The brain is lodged in a cartilaginous cranium, together with a 

 portion of the oesophagus, from which it is separated by the mem- 

 brane analogous to the dura mater : the same strong membrane 

 protects the brain where the cranium is open anteriorly. Between 

 that part of the fibrous membrane which lines the cerebral cavity and 

 the pia mater covering the brain, 

 there is an intervening space 

 filled with a gelatinous and oily 

 arachnoid tissue. In the cuttle- 

 fish, the super-oesophageal cere- 

 bral mass (^fig- 223, a) consists 

 principally of a cordiform body, 

 superficially divided into two 

 lateral lobes by a median longi- 

 tudinal furrow. From the lower 

 and lateral parts of this body 

 proceed the short and broad 

 optic nerves, which constitute 

 the peduncles of the large reni- 

 form optic ganglions {h\ and 

 upon each peduncle there is 

 placed a small spherical medul- 

 lary tubercle: these tubercles 

 exist also in the calamaries, but 

 appear not to be present in the 

 Octopods. 



From the inferior and anterior 

 parts of the super-oesophageal 

 mass, a thick cord descends on 

 each side of the oesophagus, 

 unites with its fellow, and di- 

 lates below that tube to form 

 the anterior sub-oesophageal 



Nervous system, Sepia officinalis. 



* CCCXXL, CCCCIV., CLXXXV., Bd. ii. p. 317. t. 32., & CCLXXA^ir, 



R R 4 



