16 THE OCEAN 



various forms of tow-nets have been devised. 

 Those used during the " Challenger " and 

 other early expeditions were simply long bags 

 of muslin or bunting or silk, tapering from the 

 metal hoop forming the mouth, about a foot 

 in diameter, to the opposite closed end of the 

 net. They were towed horizontally, with a 

 weight fixed on the line a short distance in 

 front of the opening, or vertically by being 

 tied to the sounding or dredging line (see 

 Plate I. ). Subsequently much larger nets and 

 pelagic trawls have been employed, and many 

 attempts have been made to construct nets 

 and traps that could be opened and closed at 

 any desired depth. The material of which 

 such nets is now made is the same as that 

 used by millers in separating the various grades 

 of flour ; it is a fine silk, made with meshes 

 of various sizes, the finest make having about 

 6000-6500 meshes to the square centimetre. 

 The meshes are pentagonal in shape, and the 

 web is so constructed that they are not easily 

 distorted. 



During the recent " Michael Sars " Expedi- 

 tion various nets, both open and closing, and 

 pelagic trawls were used with varying success, 

 but the best results were obtained by towing 

 simultaneously for long distances a number of 

 pelagic appliances (sometimes as many as 

 ten) attached to two lines at certain definite 



