Anatomy of the Food Mollusks 23 



the same time it gathers up waste material resulting from 

 muscular activities, and as it flows through the walls of 

 the excretory organs, or kidneys, certain cells of the 

 latter have the power of removing these substances. 



The heart is situated on the dorsal side of the body 

 under the hinge of the shell, in Venus. By opening the 

 delicate wall of the chamber in which it lies, it is seen to 

 be made up of three parts. On the mid-line of the back, 

 is a large sac, with filmy muscular walls, which is called 

 the ventricle. It is by the contraction of these walls that 

 blood is forced to various parts of the body through two 

 arteries, one running forward, and the other backward. 

 Joining the ventricle on either side are two auricles, sacs 

 even more filmy and delicate. Their office is to pump into 

 the ventricle blood which they receive from the gills. 



It has been stated that the intestine courses through the 

 ventricle from before backward. This is true of the 

 clams and of most other bivalves. But in the oyster and 

 scallop, the heart has been moved to a position below the 

 intestine. The oyster's heart may very easily be found by 

 picking away the thin wall just in front of the large ad- 

 ductor muscle so as to expose it as it lies in its chamber 

 (Figure 3). It is the common belief among oystermen 

 that the adductor (pa) itself is the heart, and that when 

 it is cut, the animal is at once killed. The fact is that if 

 one valve of the shell is very carefully removed, and the 

 animal is placed in a favorable current of water, it will 

 continue to live for days. 



The Excretory System. The organs for removing 

 waste matters formed as a result of muscular and other 

 activities are usually difficult to observe. In the simplest 

 cases among our edible mollusks, they are dark colored 

 tubes, one on each side of the mid-line of the body, open- 



