MOLLUSCA 51 



his tongs are full and then lift them up and empty them in the boat. 

 The size of the tongs varies, the shortest handles being about 12 feet. 

 They are used by the poorer oyster men, often in water too shallow 

 for larger dredging boats. While 10 to 15 feet is the usual depth, they 

 may be used in water as much as 30 feet deep. Needless to say tonging 

 is very hard and, in cold weather, very exposing work. 



The more modern and much more rapid method of collecting oysters 

 is by means of the dredge, an iron frame with a heavy net behind to 

 hold the oysters that the frame detaches from the bottom. The dredge 



FIG. 33. Oyster tongs. Laboratory employees tonging and culling oysters in 

 Louisiana. (After J . L. Kellogg, Shellfish Industries.) 



is used on larger sailing or steam vessels and may be hauled, by steam 

 power, Fig. 34, from any depth at which the oysters are found. "Oys- 

 ters that grow on trees" are a curiosity of the tropics, they are simply 

 oysters that become attached to the submerged roots of aquatic trees 

 (i.e., mangrove). The small mangrove oysters of the West Indies are 

 collected and sold in considerable numbers. 



As noted above the oyster in feeding will take into itself any disease 

 germs that may be in the surrounding water. The germs that enter 

 the digestive tract are doubtless soon destroyed, but where present in 



