100 THE GASTROPODA 
Bullomorpha, Thecosomata, and Heteropoda. During hibernation 
the heart of Gastropods does not beat more than twice a minute. 
The Gastropods in general have a well-developed arterial 
system, but the venous system is for the most part lacunar. A 
single artery takes its origin from the end of the ventricle opposite 
to the auricle—or from the posterior end of the ventricle in 
diotocardiate Rhipidoglossa—but in the Docoglossa (Fig. 82) one of 
its branches, namely, the 
genital artery, appears to 
have a distinct origin, as in 
the Cephalopoda. An intra- 
pericardial aortic bulb is 
found at the origin of the 
aorta in Putella (Fig. 80, V), 
various species of Fissurella, 
Ampullaria, Natica, and the 
Heteropoda, and a similar 
Fic. 80. but extra - pericardial bulb 
Heart of Patella vulgata, the auricle and ventricle in Stphonaria. In certain 
opened. I, ‘‘ branchial” vein ; [I, auriculo-ventricular 
valve; III, posterior aorta; IV, valve between the Heteropoda, ‘Thecosomata, 
ventricle and the aortic bulb; V, aortic bulb; VI, Tess : 
anterior aorta; VII, ventricle, with its internal and Nudibranchs there IS a 
muscule cola: VUTL aunels 1% pore laine valve at the origin of the 
cavity. (After Wegmann.) aorta. The ramifications of 
the aorta form an arterial 
system extending throughout the body, which is continued into a 
system of interorganic lacunae, without epithelial walls, into which 
the arterial trunks sometimes open suddenly by contractile orifices ; 
for instance, the cephalic artery of Patella and Haliotis, the pedal 
artery of Heteropods, the cephalic artery of ‘Thecosomata, ete. 
The venous blood is collected from the lacunar system into two 
large and important sinuses—an anterior or cephalo-pedal sinus and 
a posterior abdominal or visceral sinus. These two blood-spaces 
open into an anterior abdominal sinus lying beneath the pericardium. 
From the last named the blood is carried to the roof of the pallial 
cavity for oxygenation, on the right side by the rectal sinus 
(external to the rectum), on the left side by the more or less well- 
defined lateral sinus which runs along the anterior border of the 
mantle, and forms the “ pulmonary artery” in Pulmonata. Thus 
the venous section of the circulatory system ends in regular vessels, 
and in Aplysia the great abdominal sinus may be seen to open 
abruptly, by gaping orifices, into the afferent branchial vessel. The 
blood is carried from the rectal sinus to the respiratory apparatus 
by a transverse vessel or by a vascular network which generally 
forms an afferent branchial sinus running along the whole length of 
the branchia on the right side. But a very large part of the 
venous blood, larger in the archaic than in the more specialised 
