THE CEPHALOPODA 307 
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 (oxyhaemocyanin), 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 
MND NONGOO 
ee a a= 
Fia. 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 ; ¢.b, branchial heart ; ¢c.v, capsule of the branchial heart ; mp, external aperture of 
the right renal sac ; r.d.v.c, right descending branch of the vena cava; 7.s.v.c, left descending 
branch of the vena 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 ; w.k, 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.d) 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, Br; 276), their free ends pointing 
towards the head. Nautilus, the only living representative of the 
