The Clam. 43 



loBt, we snspend one or two shells in a dilate Bolntion of acetic, 

 or hydroohlotic aoid, which will remove the lime. 



The valves are held together by a hinge at the beak. 

 On the inside of the hinge is a brown, horny substance, 

 the ligament. By slowly opening and closing the shell 

 several times, we discover that the ligament (Fig. 3, 1} is 



Fig. 2. Fig. 3. 



compressed when the shell is closed (Fig. 3), but, being 

 elastic, it forces the valves apart when tbe pressure is 

 removed. On the left valve is a small shell-like tooth, 

 and a corresponding socket on the right one. 



The olasB now draw the oatside of one valve, writing on the 

 drawing the names of all the parts they have seen. 



Fig. 3, section through a clam-shell ; /, the ligament; m, one of 

 the masclea that draw the valvea together. 



Lesson II. 



In addition to the sheila already studied, children who are old 

 enongh may have freshly killed olams in which only the adductor 

 mnacles have been oat. Specimens pat into warm water the day 

 before the lesson, will die with siphon extended. The teacher 

 needs also a living clam. 



We first examine the shells that were left in dilate acid : 



These shells are soft. They will bend easily. There 

 is no lime in them, but they seem to be made of flesh. 

 Clam shells are made of layers of flesh and layers of lime. 



We remove the left valve now and examine the inside : 



