170 ALEXANDER AGASSIZ 



The chief appliances used by the oceanographer in 

 collecting specimens are the dredge, the trawl, the tan- 

 gles, and the tow net. Up to that time the dredge used 

 by the Danish naturalist 0. F. Miiller, in the eighteenth 

 century, a modification of the old oyster dredge, had 

 undergone but slight modifications. The naturalist's 



Dredge 



dredge consists of a framework of what would be the 

 edges of a broad shallow box. To one end of the frame, 

 which is considerably heavier, a bag of netting is at- 

 tached and a heavy canvas is stretched over the frame, 

 leaving the towing end of the dredge open, to which 

 the mouth of the bag is attached. Dredges as then made 

 had beveled edges at the open ends of the frame. Such 

 dredges, when drawn over muddy bottoms, brought up a 

 great amount of mud. To obviate this defect, Agassiz 

 bound stout rope about the forward framework so that 

 the lips should not cut into the mud, and subse- 

 quently his dredges were made with flat frames, which 

 completely obviated the defects in the old-fashioned 

 models. 



The trawl is by far the most useful instrument in 

 deeper water, where the bottom generally consists of 

 ooze or fine mud. Before Agassiz's day, the form used 

 in deep water was the ordinary beam trawl of fisher- 

 men. This consists of a beam on runners, to which is 

 fastened a long V-shaped net. In shallow water this 

 trawl can be so weighted as to fall on the runners, but 



