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Biology in America 



to the lower and larger of which is attached the net proper, 

 composed of fine bolting cloth, and terminating below in the 

 detachable bucket which receives the catch. To relieve the 

 strain on the silk this bucket may be supported by strings 

 attached to the larger ring above and the silk may be sur- 

 rounded by netting to protect it from injury. The object 

 of the inverted cone is to insure the passage of all the water 

 through the net which enters its mouth, a large part of which 

 would otherwise flow over the edge of the net, rather than 



HENSEN'S NET 

 For collecting plankton in the sea. From Steuer after Chun. 



through its meshes, due to the resistance of the latter to the 

 water. By lowering the net a given distance and then hauling 

 it to the surface Hensen expected to filter all but the most 

 minute organisms out of a column of water, whose height 

 was the length of the vertical haul, and whose diameter was 

 the diameter of the net opening. In this way he attempted 

 to compute the number of organisms present beneath any 

 given area of the sea's surface down to any given depth. 

 Experiments have shown however that not all of the water 

 assumed to pass through the net does pass through, and that 



