CIRCULATORY SYSTEM OF THE GIANT SCALLOP. 23! 



The systemic veins (Fig. 4) that collect the blood that is sup- 

 plied by the systemic arteries, from the various organs of the body, 

 may be injected from several different vessels. They may be in- 

 jected by pushing the needle beneath the membrane that covers 

 the posterior surface of the adductor muscle. A large blood 

 space occupies this position, into which the needle is inserted and 

 the mass injected fills the systemic veins. Another point from 

 which these veins may be injected is from one of the superficial 

 vessels of the visceral mass. These vessels are very conspicuous, 

 and may be very easily picked up with the needle. Still another 

 vessel is the vein that returns blood from the liver, which may 

 be seen on the left side of the animal anterior to, but near the 

 large artery that supplies the liver. Injecting any one of these 

 vessels will to a greater or less extent inject the others, but there 

 does not seem to be an entirely free communication between 

 them. They all carry blood to the kidneys, and seem to empty 

 into a common sinus on either side, that lies alongside the kidneys 

 in the walls of the visceral mass. The sinuses of the two sides 

 are connected beneath the adductor muscle, but it frequently hap- 

 pens that a complete injection of the system is not obtained from 

 an injection from any one of the veins mentioned. Just where 

 the obstruction lies in such cases has not been determined. It 

 has been noticed that obstructions are more likely to be encoun- 

 tered in injecting from the veins of the visceral mass than in in- 

 jecting from any of the others. 



Inasmuch as blood spaces are cut in removing the muscle from 

 the shell, it has been found desirable in injecting this system of 

 vessels to wedge the valves open and to inject from the posterior 

 surface of the adductor muscle. In injecting after the animal is 

 removed, a considerable quantity of the injecting mass is sure to 

 escape at the ends of the muscle. 



The position of the veins may be seen in Fig. 4. A large vein 

 comes from the liver, another from the foot, and the veins in the 

 muscle unite to form a more or less definite sinus along the dor- 

 sal border of the muscle, and two smaller ones on the antero-ven- 

 tral side of the muscle. These sinuses unite near the anterior ends 

 of the kidneys. A series of vessels from the visceral mass unite 

 along the borders of the kidneys and finally connect with these 



