LOLTGO PEALEII. 149 



The blood that is received by each branchial heart is sent 

 into the corresponding gill through a branchial artery that leaves 

 the heart near the opening of the mantle vein, and runs along 

 the side of the gill that is attached to the mantle. 



The blood is collected from each gill by a large branchial vein 

 that runs along the ventral side of the gill, and enters the sys- 

 temic heart. 



Draw a figure showing the vessels connected with the branchial 



hearts. 



Expose the systemic heart by carefully removing the superfi- 

 cial tissue between the branchial hearts, and notice that it 

 is not symmetrical. Its lateral angles receive the branchial 

 veins and it gives rise to an artery from each of the other two 



angles. 



1. The posterior aorta divides almost immediately into three 



large vessels. These are: 



(a) The median mantle artery which follows the edge of the 

 ventral mesentery to the mantle. 



(6) A pair of lateral mantle arteries which diverge posteriorly 

 and supply the two sides of the mantle. Besides these large 

 vessels there is a small vessel that runs anteriorly over the ven- 

 tral surface of the heart and supplies the ink gland and rectum, 

 and another one that runs dorsally and posteriorly to supply part 

 of the reproductive system. 



2. From the dorsal surface of the heart, near its anterior 

 end, a small vessel passes over the anterior and dorsal surfaces 

 of the stomach and finally passes into the gonad. 



3. The anfmor aor to is larger than the posterior aorta. From 

 the anterior angle of the heart, which is to the right of the median 

 line, it follows a straight course^ alongside the esophagus to the 

 head. A number of small vessels are given off along its course, 

 and it is finally distributed to the head and arms. 



Draw the vessels connected with the systemic heart, into the 

 figure you have just made. 



Nervous System.— The stellate ganglia may be seen through 

 the transparent lining of the mantle, on either side of the neck, 



