THE CEPHALOPODA 305 



posterior part of the mantle, including the siphonal prolongation of 

 Nautilus and Spirilla and the fins of the various Dibranchia ; (3) a 

 small genital artery, which may originate from the abdominal aorta 

 (Fig. 277, g.a), or separately from the ventricle : it may even be 

 triple, as in Nautilus, where there is one artery for the gonad, one 

 for its duct, and one for the homologue of the duct, the pyriform 

 appendage. 



In Nautilus the circulation is partly lacunar, except in the 

 integuments, but in the Dibranchia the vascular apparatus is 

 remarkably perfect, and sinuses are, as a rule, absent, the blood 

 passing from the arteries into the veins through the intermediary 

 of capillary vessels provided with an endothelium. Nevertheless, 



vent 



n \ I \ \ *' ~" -\ .\ re f 



Tula- vise .per. 

 aperb. 



FIG. 271. 



Diagram representing an approximately median sagittal section of Sepia offitiiialis ; this 

 drawing is intended to be compared with the foregoing one. a, internal shell ; a.b.v, afferent 

 branchial vessel; an, anus ; app, appendage of the branchial heart ; b, nuchal cartilage; br.b, 

 branchial heart ; c, the integument covering the visceral hump ; cr, crop ; ct, the left ctenidiuzn ; 

 d, the reflected portion of the mantle-skirt forming the sac which encloses the shell ; e, the 

 inferior margin of the mantle-skirt ; e.l.v, efferent branchial vessel ; /, the pallial chamber ; g, 

 the vertically cut median portion of the funnel ; gizz, the gizzard ; i, the valve of the funnel ; 

 i.s, ink-bag ; m, the two upper lobes (arms) of the foot ; n, the long prehensile arms ; n.c, the 

 nerve-collar; n.n.u, aperture of the left kidney; o, the fifth or lowermost lobe (arm) of the 

 foot ; p, the third arm ; </, buccal membrane ; re, renal glandular mass ; s, the lower jaw ; t, the 

 radula ; v, the upper jaw ; i*wt, ventricle of the heart ; visc.per.apert, viscero-pericardial aperture ; 

 x, the viscero-pericardial sac. (After Lankester.) 



in the Octopoda there is a large venous sinus on the course of the 

 blood returning to the gills : this sinus surrounds the oesophagus 

 and salivary glands, the hepatic ducts, the anterior aorta, etc., and 

 communicates by a large venous trunk with the great vena cava 

 which carries to the gills the greater part of the blood coming from 

 the body. In Nautilus the whole visceral cavity is a vast blood- 

 sinus communicating with the vena cava by a number of perforations 

 in the walls of the latter vessel, in the same manner as, in Aplysia, 

 the abdominal sinus communicates with the afferent branchial vein. 

 The vena cava of Cephalopods consists of a principal trunk directed 

 antero-posteriorly : this trunk in Nautilus (Fig. 274, v.c) is divided 

 into four, and in the Dibranchia into two afferent branchial veins, 

 each of which is joined by a pallial and an abdominal vein (Fig. 



