26 



NERVES OF CEPHALOPODS. 



also terminate in ganglia, 

 from which arise a great 

 many filaments. In the tetra- 

 branchial cephalopods, the 

 oesophageal collar is simply 

 protected by the cephalic car- 

 tilage; but in the dibranchial 

 cephalopods, in which the 

 nervous system acquires its 

 highest degree of develop- 

 ment, this medullary mass 

 is lodged in a special cavity, 

 hollowed in the cartilage 

 through which the oesopha- 

 gus passes. 



13. The cephalopods are 

 never hermaphrodite, as are 

 most others of the mollusca. 

 The ovary is always simple 

 and lodged at the bottom of 

 a sac formed by the body of 

 the animal ; sometimes there 

 is but a single .oviduct ; at 

 others, we find two, which 

 open at the base of the fun- 

 nel ; finally, all these ani- 

 mals are oviparous. 



14. All these mollusks 

 are marine : they are very 

 voracious, and feed chiefly 

 on Crustacea and fishes, 



which they seize by the aid of their supple and vigorous arms, 

 and easily devour by means of their sharp mandibles. Their 

 flesh is eaten. 



15. This class is divided into two families. 



Fig. 11. NERVOUS SYSTKM OF 



THE NAUTILUS. 



Explavation of Fig. 11. — Nervous system of the Nautilus : — c. the brain; 

 — 0. the optic nerves ; — g. the sub-cesophag-eal or thoracic g-anglia, ; — t. the 

 tentacular g'angHa ; — p. nerves of the tentacula ; — e. the nerves of the funnel ; 

 — a. a gangUon from which arise other teiTtacular nerves (/>) ; — d. a second, 

 and similar ganglion, also giving rise to tentacular nerves (/) ; — in. nerves 

 of the mantle, «fec. — v. the great visceral nerves, each of which gives rise to 

 a ganglion (gv), from which the principal nerves of the viscera take their 

 origin. 



13. Do cephalopods lay eggs? 



14. Where are cephalopods found ? Upon what do they feed ? 



15. How is the class of cepkalopods divided ? 



