The systemic veins (fig. 14) 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 injected by pushing the needle beneath the mmbrane 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 kidney in the walls of the visceral mass. The sinuses of 

 the two sides are conneected beneath the adductor muscle, but 

 it frequently happens that a complete injection of the system is 

 not obtained from an injection from any one of the veins men- 

 tioned. Just where the obstruction lies in such cases has not 

 been determined. It has been noticed that obstructions are more 

 likely to be encountered in injecting from the veins of the vis- 

 ceral mass than in injecting 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 figure 14. 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 dorsal border of the muscle, and two smaller ones on 

 the anterior and ventral side of the muscle. These sinuses unite 

 near the anterior end of the kidneys. A series of vessels from 

 the visceral mass unite along the borders of the kidneys and 

 finally connect with these sinuses. Most of the blood from all of 



39 



