58 



the veins bringing Mood back from all parts to the renal 

 organ. They can be seen by removing the auricle and 

 ventricle from the pericardium , and by slitting the renal 

 organ along its left ventral margin and thus laying bare 

 its internal surface. 



3. — The syringe should be inserted into the aorta 

 (figs. 35, 36, Ao.) at the point where it leaves the ventricle. 

 This injection should be performed with the hot jelly, but 

 it is the most difficult one and often fails. The arterial 

 system is injected by this means. 



The Heart. 



Buccinum possesses (as do all Monotocardia so far as 

 is known, except Cypraea) only one auricle (the left one 

 of the lower Gastropods). 



The auricle and ventricle lie in the pericardial cavity, 

 which is bounded by the renal organ and the digestive 

 gland, the auricle being anterior. 



The auricle is a very thin-walled sac, capable of 

 considerable extension. It is somewhat like a pear in 

 shape with the pointed end situated ventrally, and into 

 this end opens the efferent branchial vessel. 



There are two other openings into the auricle which 

 are situated at the dorsal end. One of these at the anterior 

 edge of the pericardium is the opening of the nephridio- 

 cardiac vein, the other, which is situated on the posterior 

 surface, is the opening into the ventricle. The latter, 

 the auriculo-ventricular passage, is guarded by a valve 

 so that blood is prevented from passing backwards from 

 ventricle to auricle. 



It will be noticed that the nephridio-cardiac vein 

 opens directly into the auricle and not into the efferent 

 branchial vessel. It is often somewhat difficult, however, 

 to determine whether the vein enters near the opening of 



