OYSTERS, CLAMS, AND OTHER MOLLUSKS 235 



The drill is another dangerous enemy of the oyster. 

 This little shell-fish belongs to the conch family and 

 looks a great deal like a periwinkle. It has a spiral 

 drill like an auger and bores through the oyster's 

 shell, thereby killing him. If drills attack an oyster 

 bed, about the only thing to be done is to move the 

 valuable shell-fish to another bottom. 



When the oysters are about two years old they are 

 transplanted. The oysterman attempts to spread 

 them out so that all of them have room to grow. Care 

 must be used in handling oysters, or they will be in- 

 jured, and a considerable number will be lost. 



The oysterman must not only watch the living 

 enemies of the oyster, but he must also guard his 

 waters from pollution by sewage and trade wastes 

 turned into the bays by towns and factories. Many 

 wastes from chemical plants will kill the larvae before 

 they settle to the bottom, and some will destroy fully 

 groTSTi oysters. 



Pollution by sewage seldom kills oysters, but it 

 renders them unfit for consumption. The fine strain- 

 ing apparatus of the oyster takes from the water 

 many bacteria and other microscopic organisms ; and 

 if the w^ater contains disease germs, such as those 

 which are found in sewage, they may be found in 

 the oysters living in the polluted waters. Recently a 

 method of disinfecting living oysters has been in- 

 vented by which the oysters are treated with small 

 amounts of chlorine. 



Oil from vessels of all sorts floats on the surface 

 of all harbors which have much shipping. This oil 

 forms a thin, nearly continuous film which prevents 



