4() 



ON CLASSIFICATION. 



fundamental characters. Thus, the mantle is related to the 

 body, as in Pterojwla and Gasteropoda ; when an external shell 

 exists it is composed of a single piece, and the Cephalopocls have 



Vis. Iti. 



Fig. 16. — Diagrammatic section of a female Cephalopod (Sepia officinalis), a, Buccal mass 

 surrounded by the lips, and showing the horny jaws and tongue ; 6, oesophagus ; c, 

 salivary gland; d, stomach ; e, pyloric caecum ; /, the funnel ; g, the intestine ; h, the 

 anus ; i, the ink-hag; k, the place of the systemic heart; Z, the liver ; 'n, the hepatic 

 duct of the left side ; o, the ovary ; p, the oviduct ; q, one of the apertures by which 

 the atrial system, or water-chambers, are placed in communication with the exterior ; 

 /•, one of the branchiae ; s, the principal ganglia aggregated round the oesophagus ; in, the 

 mantle ; sh, the internal shell, or cuttle-bone. 1, 2, 3, 4, 5, the produced and modi- 

 lied margins of the foot, constituting the so-called "arms" of the Sepia. 



an odontophore constructed upon just the same principle as 

 that of the other classes. The nervous system, the foot, and 

 the epipodia exhibit the same primary relations as in these 

 groups, and there is a distinct head, with ordinarily well- 



