65 



that the latter become gradually smaller towards the apex of the gill. Each of 

 the alternating branches of the branchial artery (VIII) passes around the canal 

 of the gill and joins a zigzag longitudinal artery (l 8 ) which is on the same side 

 of the canal with the branchial vein and so opposite the artery. In this way 

 the canal is surrounded by a series of alternating semicircular vessels which 

 unite the longitudinal arteries. Near the middle of each semicircular vessel the 

 larger portion of each branch of the branchial artery passes out at right angles 

 to the canal and forms the outer edge of a pinna. 



The branchial artery and vein , the anterior and posterior vena cava , and 

 the larger branches of these vessels are peristaltically contractile. 



Dhrere has found that the oxygen-carrying power of the blood of cephalopods 

 is directly proportional to the amout of copper in the blood. The blood coagula- 

 tes readily and firmly. The blood corpuscles are not numerous in the blood and 

 they resemble the lymphocytes of higher animals. 



