THE OYSTER. 



Oysters in the shell should be used. Find the hinge as 

 in the clam, Do you find lines of growth ? In the same 

 way as in the clam distinguish anterior and posterior, right 

 and left valves. Is the right or the left valve convex ? 



Break the shell at the hinder end and, inserting a knife, 

 cut the adductor muscle so as to remove the left valve.* 

 How many adductors do you find ? Is the mantle edge 

 thickened and united as in the clam ? Do you find any 

 siphons ? What other peculiarities do you find in the edge 

 of the mantle ? 



Remove the mantle from the left side and trace the parts. 

 How does the foot compare with that of the clam ? How 

 do the palpi differ ? How many gills ? Which adductor 

 anterior or posterior is absent ? Find the heart, just in 

 front of the adductor. Lay open the pericardium. How 

 many auricles and how many ventricles are present ? Trace 

 the alimentary canal through the body from the mouth to 

 the vent. How is it related to the heart ? 



* If you do not know where the adductor is, study a shell already 

 removed and find the scar made by it. 



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