VENUS MERCENARIA Linnams 



Material. Live specimens of Venus mercenaria may be 

 bought on the market under the name of hard shell clam. To 

 open them they must be placed for several minutes in water 

 heated to 70 centigrade. After that they should be preserved 

 in weak formalin. Freshly killed specimens should be injected 

 and preserved in formalin for the study of the digestive organs. 

 The following is the best method. The left valve is removed in 

 the usual manner. The animal in its right valve is placed in a 

 dish with warm water. A hypodermic syringe is introduced into 

 the rectum a little in front of the anus and the injection con- 

 tinued until the mass begins to come out through the mouth. 

 The best mass to be used is a solution of gelatine in water made 

 dark red by the addition of finely powdered carmin. When the 

 injection is finished, the specimen is placed in 4% formalin which 

 gradually hardens the injection mass and makes it insoluble. 

 Every student should receive one freshly killed and injected 

 specimen. For the additional exercise, transverse sections 

 through hardened specimens should be studied under water. 



Descriptive Part 



Venus mercenaria is a common representative of the Class 

 Lamellibranchia which comprises all bivalves. It lives in the 

 mud, between tides, along the Atlantic Coast. In its structure 

 it is strictly bisymmetrical, the valves being right and left and 

 their hinge dorsal in position. The anterior or oral end of the 

 body may be recognized by the fact that it is broader and that the 

 lines of growth of the shell are procurved. The starting points 

 of growth in the two valves are called umbones; the first lines of 



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