258 MOLLUSCA. CEPHALOPODA 



exterior, and behind into the mantle-cavity (c) ; this may 

 be either a perfect tube or may be formed by the apposi- 

 tion of two trough-like lobes. By some authors the arms 

 or lobes around the mouth are regarded as the fore-foot, 

 and the funnel as the mid-foot, the hind-foot being absent. 



h i 



Fig. 102. Diagram of a vertical median anteroposterior section of Sepia 

 officinalis, a, shell ; b, mouth of mantle-cavity ; c, mantle-cavity ; 

 d, funnel ; e, arms ; /, long arm ; g, the upper beak or jaw; h, the 

 lower beak or jaw ; i, odontophore ; k, the viscero-pericardial sac ; 

 I, the nerve-collar ; m, the crop ; n, the gizzard ; o, the anus ; p, left 

 gill; q, ventricle of the heart; r, renal glandular mass; s, left 

 nephridial aperture ; t, viscero-pericardial aperture ; u, branchial 

 heart ; iv, ink-sac. (After Lankester.) 



Others, however, consider that the funnel alone represents 

 the foot. The name Cephalopoda is due to the former 

 view — that the foot has grown round the mouth and is 

 divided up into arms or lobes. The part of the body near 

 the mouth and funnel is usually regarded as ventral, and 

 the opposite part as dorsal. 



On the upper surface of the head there are two large 

 eyes, which, except in Nautilus, are almost as highly 

 developed as in vertebrate animals. The mantle is formed 

 by a single fold of the skin, which passes quite round the 

 body; on the anterior (upper) surface the fold is very 

 shallow so that the mantle-cavity exists mainly on the 



