Ce2}halopoda — Dihranch tat a. 



11 



■with the external shell commonly met with in all the other Spirula. 

 raollusca; and although it is apparently internal in the squids, CrAMiERY 

 cuttles, and calamaries, it is in reality always enclosed in 

 a sac, or a fold, or lobe of the mantle which secretes the shell. 



Fig. 27. — Spirula Peronii, Lamk. New Zealand, a, the animal with the shell Table-case 

 in situ ; b, the shell removed from the animal ; c, the shell laid open 67. 

 to show the septa, {a, | nat. size ; b, c, nat. size.) 



k 



The nervous system is more concentrated than in the other 

 mollusca, and the larger ganglia are protected by a cartilage. The 

 respiratory organs consist of two or four plume-like gills, placed 

 symmetrically on the sides of the body in a large branchial or 

 ruantle-chamber opening forwards on the underside of the head : 

 in the middle of this opening is placed the siphon or funnel. The 

 sexes are distinct in all living Cephalopods. In Nautilus only, 

 the males are less numerous than the females. 



The Cephalopoda have been divided into two orders, based upon 

 the number of the gill-plumes present in each ; but they present 

 besides several other important characters by which they can 

 be distinguished and classified. 



1. — DiBEANCHiATA (two-gillcd division). Cephalopods having the 

 inflected margins of the mid-foot fused together, so as to form 

 a complete tubular funnel. The lobes of the fore-foot, which 

 surround the mouth, carry suckers disposed in rows. They have 



