THE CLAM 129 



the posterior aorta, which carry blood to different regions. 

 Veins return the blood to kidneys, gills, and auricles. 



2. Excretory System. The kidney is a dark greenish 

 gland on either side of, and ventral to, the pericardial sac. 

 Each kidney is a wide thin-walled tube, doubled on itself 

 so that the two ends are close to each other. These ends 

 are anterior and about opposite, and ventral to, the anterior 

 end of the pericardium, while the loop is posterior and lies 

 against the posterior adductor muscle. One end of the 

 kidney opens into the pericardium, the other into the cavity 

 of the inner gill. 



3. Nervous System. This system is composed of three 

 pairs of ganglia connected by nerves. First locate the 

 visceral ganglion just under the posterior adductor muscle. 

 It will appear as a yellowish mass under the skin which 

 covers the muscle. How many nerves arise from this center? 

 To what regions or organs do they go? A small nerve on 

 either side extends forward from this mass to the brain. 

 The brain or cerebral ganglia will be found just under the 

 palps above the mouth, one on either side. From this nerves 

 extend to the adductor muscle, mantle and palps. Also 

 a nerve, the cerebral connective, connects the two ganglia. 



The pedal ganglia are a fused pair in the foot and are 

 joined to the cerebral ganglia by connectives. These ganglia 

 will be found while working on the digestive system. 



4. Digestive System. With a razor split the foot and the 

 visceral mass vertically in the median line. Identify the 

 following parts: The mouth is immediately behind the 

 anterior adductor muscle. From this a short esophagus 

 leads to the stomach, which is in the dorsal part of the body. 

 Note the greenish digestive gland, or liver, surrounding the 

 stomach. The intestine extends from the ventral side of 

 the stomach to the ventral part of the foot, then poste- 



