ioo 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 -de. /eloped 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 Patella (Fig. 80, V), 

 various species of Fissurella, 

 Ampullaria, Natica, and the 

 Heteropoda, and a similar 

 but extra - pericardial bulb 



Heart of Patdlti vulgata, the auricle and ventricle in Swhonaria. In Certain 



opened. I, "branchial" vein; II, auriculo- ventricular TT j m i 



valve; III, posterior aorta; IV, valve between the Heteropoda, IhCCOSOmata, 

 ventricle and the nortic bulb ; V, aortic bulb ; VI, i XT A -v. u *u 



anterior aorta ; VII, ventricle, with its internal and Nudlbranchs there IS a 



muscular columns ; VIII, auricle ; IX, pores leading valvp at trip oricn'n nf flip 



into the auricle the blood of the roof of the pallia! VaiVG ai tne 



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, etc. 

 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 



