Mollusca. 



57 



tious without the aid of a teacher, he will find directions for 

 opening clams, without using hot water, in the Suggestions to the 

 Teacher of Zoology, in a separate pamphlet. 



Put the live clam for a few minutes into water as warm as the 

 hand can well bear. This causes the muscles to relax, so that 

 the shell can be' readily opened. Pry apart the two valves, and 

 insert a half-inch block to keep them from shutting. 



1. Observe a soft white membrane, the mantle, adhering to the 

 inner surface of the shell. Look in at the posterior end for 

 the two siphon openings. Now hold the clam in the left hand, 

 with the left valve up and the ventral margin toward you. Insert 

 the chisel-like handle or the blade of a scalpel between the mantle 

 and the left valve, and gently separate them by sliding the scalpel 

 handle along the inner surface of the shell. In this way proceed 

 backward, around the posterior end of the shell, then forward 

 along the dorsal margin. Back of and below the hinge is a large 

 white muscle, which extends directly across from valve to valve. 

 Cut this off close to the left valve if it is not already severed. In 

 like manner loosen the mantle at the anterior end, and find another 

 muscle connecting the two valves near the anterior dorsal margin. 

 Sever as before, close to the left valve, and loosen the mantle 

 completely from the left valve. 



2. Press the shell shut ; now release the pressure. What makes 

 the shell spring open ? Repeat the closing and releasing until you 

 have a satisfactory explanation of the method of opening. Be on 

 the lookout later for the means by which the clam shuts its shell. 

 Break off the left valve by bending it forth and back, twisting it 

 off if necessary. 



3. Lay the clam in the dissecting pan and cover it with water. 

 Renew the water as often as it becomes turbid. To keep the 

 clam level use the left valve, hollow side down. 



Observe that the left mantle lobe now covers the body, and that 

 the right lobe lines the right valve. Notice the thicker margin of 

 the mantle. Pinch this thick edge ; if it has not already shortened 

 as much as possible it may draw up slightly. Observe a thin, 



