310 TRANSACTIONS LlVP:Er00L BIOLOGICAL SOCIETY. 



the veius bringing" blood back from all parts to the renal 

 organ. They can be seen by removing the anricle and 

 ventricle from tlie ])eri('ardinm, and by slitting the renal 

 orffan aloiiff its left ventral margin and thus lavino: bare 

 its internal surface. 



•>. — The syringe should be inserted into the aorta 

 (figs. 85, 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. 



Buccinuin possesses (as do all Monotocardia so far as 

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

 of the lower Grastropods). 



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 tlie dorsal end. One of these at the anterior 

 edge of the pericardium is the opening of the nepliridio- 

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

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

 the auriculo-ventricular passage, is guarded by a valve 

 so tliat blood is prevented from passing backwariLs from 

 \cntrich' to auricle. 



It will l)e noticed that the nepliridio-cardiac vein 

 opens directly into the auricle and not into the efferent 

 branchial vessel. It is often somewhat difficult, liowever, 

 to (h'tciniinc whether the vein enters neai the oj)ening of 



