50 BRITISH INDUSTRIES. 



that the tide may happen to take them, until it is 

 thought desirable to haul them in. When at work, they 

 are extended in a long single line, it may be one or two 

 miles in length, their upper edge being supported at 

 or near the surface by means of floats, the nets hang- 

 ing perpendicularly in the water, and forming, as it 

 were, a perforated wall or barrier many hundred yards 

 long and several yards deep. The shoals of fish, in 

 their endeavours to pass through this barrier, force 

 their heads into the meshes, the size of the mesh used 

 depending on whether herrings, mackerel, or pilchards 

 are expected to be caught, and being such as to allow 

 the head and gill-covers to enter, but not to permit 

 the thicker body of the fish to go through. When the 

 fish has found its way through the net beyond the gill- 

 covers, it may generally be considered as effectually 

 meshed ; there is, indeed, little chance of its escape, 

 for the mesh is only large enough for a fish of average 

 size to push its way so far, when the gill-covers are laid 

 close to the body ; but it is necessary for them to open 

 again that the fish may breathe, that is, that the water 

 which enters the mouth may, with the air it contains, 

 pass over the gills, and after purifying the blood with- 

 in them, just as the air we take into our lungs purifies 

 the blood they contain, escape through the gill opening 

 on each side of the head. As this is taking place, and 

 the fish is at the same time hampered by the net, the 

 mesh slips forward and catches in the gill opening, 

 from which it cannot easily be cleared without more or 

 less injury to the fish. In drift-net fishing, then, the 

 nets act as barriers to intercept the moving shoals, and 



