60 Practical Zoology. 



b. A thin sac, triangular as seen from the side, with its apex join- 

 ing the ventricle, and its base attached just above the upper edge 

 of the gills; this is the left auricle. Each auricle receives the 

 blood from the gills of the corresponding side. 



14. Just in front of the posterior adductor muscle are the dark 

 kidneys. 



15. Above the kidney, and in front of the posterior adductor, 

 is a small muscle, which extends backward from the side of the 

 body to join the valve near the posterior adductor. This muscle 

 pulls the foot upward and backward, hence is called the posterior 

 retractor muscle. 



1 6. Below and a little back of the anterior adductor muscle, 

 find the protractor muscle, which pulls the body and foot forward. 



1 7. Just above and back of the anterior adductor is the anterior 

 retractor muscle, which pulls the foot and body up and backward. 



1 8. To find the mouth, hold the clam, anterior end uppermost, 

 still attached to the right valve ; press down the point of the foot, 

 and find the mouth opening posterior to the anterior adductor; 

 observe that the two outer palps unite above the mouth, and the 

 two inner palps unite below the mouth. Back of the anterior ad- 

 ductor a dark-colored mass may be seen within the body ; this is 

 the digestive gland, which surrounds the stomach. The intestine 

 has several coils in the body before emerging on the dorsal surface 

 a short distance in front of the heart. The intestine can be traced 

 much better in an alcoholic specimen. 



19. Beginning at the posterior adductor, cut away all the free 

 flap of the left mantle lobe, following the upper edge of the gills 

 (being careful not to cut away the labial palps) to the upper edge 

 of the anterior adductor. Make a drawing of all the parts above 

 named, as they lie in the right valve. 



20. Remove all the remaining soft parts except the adductor 

 muscles. Since the chief characteristic of muscle is its ability to 

 shorten, it should now be clear how the clam shuts its shell. Turn 

 back to No. 2 of these directions and consider the relations of the 

 mechanisms for opening and shutting. What actions take place 



