THE RIVER MUSSEL 37 



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open. This is the pericardial cavity. Within it, is a dark 

 tube, the intestine, which runs straight through the cavity. 

 The ventricle of the heart surrounds the intestine about 

 midway of its length. The auricles, right and left, are at- 

 tached to the right and left sides of the ventricle, respec- 

 tively. The blood is brought to the auricles from the gills 

 by the two branchial veins, one to each auricle. It is then 

 emptied by the auricles into the ventricle. From here it is 

 forced through the anterior and posterior aortas to the differ- 

 ent parts of the body. 



On either side of the front part of the abdomen are two 

 soft, triangular flaps, the labial palpi. Between these and 

 directly in front is the mouth. It leads by a short gullet 

 to the stomach, which is surrounded by a dark mass, the 

 liver. The liver is plainly discernible. The intestine may 

 be traced from the stomach by using a bristle. It makes 

 several turns before it runs through the pericardial cavity. 

 Remove the heart and note beneath it the kidneys, or renal 

 organs. 



Beneath the posterior adductor muscle is a pair of yellow- 

 ish white ganglia. These are the visceral ganglia. They 

 give off several nerves that run to the mantle and gills. 

 Two nerves also run from the visceral ganglia to join a pair 

 of ganglia near the mouth. From the latter, a pair of nerves 

 run to the pedal ganglia, which lie deeply imbedded where 

 the foot and the abdomen meet. 



Make a drawing showing as many of these points as 

 possible. 



D. INTERNAL FEATURES OF THE SHELL. Remove the 

 body of the mussel from the shell. 



Note the color of the shell lining and its smooth, pearly 

 finish. 



