THE FRESH-WATER CLAM. 53 



Look near the anterior adductor for similar mus- 

 cles ; what work do they perform ? 



13. To find the mouth, hold the clam, anterior end upper- 

 most, still attached to the right valve, in the left 

 hand ; press down the point of the foot, and find the 

 mouth opening below the anterior adductor ; observe 

 that the two outer palpi unite above the mouth, and 

 the two inner palpi unite below the mouth. Back of 

 the anterior adductor a dark-colored mass may be 

 seen within the body; this is the liver, which sur- 

 rounds 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. 



14. 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 palpi) to the upper edge of the anterior ad- 

 ductor. Make a drawing of all the parts above 

 named, as they lie in the right valve. 



15. Remove the remaining soft parts in as good condition 

 as possible, and put into alcohol, for the dissection of 

 the nervous system. 



16. Make a drawing of the inside of one of the valves, 

 showing the hinge, the muscle scars, and any other 

 markings that have any significance. Sometimes 

 there can be distinctly seen a line running near, and 

 parallel to, the ventral margin, along which the upper 

 edge of the thicker portion of the mantle was at- 

 tached; this is the mantle line, or pallial line. 



17. Some clams have hinge teeth, by which the dorsal 

 edges of the valves are more firmly held together 



