THE CEPHALOPODA 



37 



branchial hearts, a large part of the venous system is contractile, 

 and this is notably the case with the vena cava and its two afferent 

 branches. 



The venous blood is blue through the presence of haemocyanin, 

 which becomes colourless on oxidation (oxy haemocyanin). The 

 pressure of the blood in the arteries of the Cephalopoda is very 

 considerable and exceeds that of some Vertebrates : in Octopus it 

 amounts to eight centimetres of mercury. In the head of the 



Fio. 273. 



Diagram of the renal sacs, and the veins which run through them, in Sepia officinalis ; ventral 

 view, the upper walls of these sacs are supposed to have been removed, a.r, glandular renal 

 outgrowths ; c.b, branchial heart; c.v, capsule of the branchial heart ; np, external aperture of 

 the right renal sac.; r.d.v.c, right descending branch of the vena cava ; r.s.v.c, left descending 

 branch of the veria cava ; v.a.d, right abdominal vein ; v.a.s, left abdominal vein ; v.b.a, vein 

 from the ink-bag ; v.c, vena cava ; v.g, genital vein ; v.m, mesenteric vein ; v.p.d, right pallial 

 vein ; v.p.s, left pallial vein ; iv.Tc, viscero-pericardial sac (dotted outline); x, appendage of the 

 branchial heart ; y, y', the left and right reno-pericardial orifices. (From Lankester, after 

 Vigelius.) 



Dibranchia there is a lymphatic gland near each eye : this gland is 

 known as the "white body" (Fig. 268, w.b) and is the remains of 

 a degenerate portion of the central nervous system of the embryo. 



The branchiae or ctenidia are situated in the pallial cavity on 

 either side of the visceral mass. They originate posteriorly in the 

 embryo, between the mantle and the foot (Fig. 257, gi), and after- 

 wards sink in towards the bottom of the pallial cavity where their 

 axes are inserted (Figs. 272, Er ; 276), their free ends pointing 

 towards the head. Nautilus, the only living representative of the 



