120 MOLLUSC A. 



and anterior to the anus. If possible, insert a guarded bristle 

 into this opening and see what becomes of it. Trace the oviduct 

 from the ovary along the columellar side of the liver. See what 

 becomes of it. Examine the inside of the nidamental gland 

 and see its relation to the oviduct. 



If the specimen is a male, follow the vas deferens from the 

 testis to the base of the penis. 



Circulatory System. Remove the thin membrane that forms 

 the roof of the pericardial chamber. 



1. The heart consists of : (a) the large, rounded ventricle; 

 (b) the smaller, conical, thin-walled auricle. 



2. The auricle receives blood by two vessels. One, return- 

 ing blood from the gill, runs along the left side of the gill to its 

 posterior end, where it bends abruptly to the right along the 

 margin of the pericardial cavity, and enters the auricle. The 

 other returns blood from the tubuliferous portion of the kidney 

 and follows the right side of the pericardium to the auricle. 



3. The gill receives its blood through a vessel that borders 

 its right side. This vessel receives the blood from a portion of 

 the mantle, and from the large, acinous portion of the kidney. 



4. The blood leaves the ventricle by a single vessel, the aorta, 

 that almost immediately gives rise to the visceral artery which 

 supplies the visceral hump. Trace its distribution. 



The aorta makes an abrupt turn downward and forward and 

 enlarges to form the secondary heart which lies alongside the eso- 

 phagus. Follow the course of the aorta and its branches. 



The course of general circulation is, beginning with the heart, 

 (a) system, (b) kidney, (c) gill, and (d) back again to the 

 heart. Why is such a course of circulation better than the 



reverse 



Draw a figure showing the vascular system. 



Excretory System. The two portions of the kidney have 

 already been noticed. Cut along their common line of union 

 and examine the inner surface of each part. 



1. Notice the parallel lines of tubules that form the substance 

 of the tubuliferous portion, and the lobules that form the com- 

 paratively thick walls of the acinous portion. 



