CH. l] 



THE EXPLORATION OF THE SEA 



27 



off into a bottle of water and these are then studied fresh or are 

 preserved. With fine material, such as fine silk, the tow-net 

 catches little and the catch is always small ''fry." This is because 

 of the restricted " draft " of water through the meshes of the net. 

 With nets made of coarser material more may be caught but 

 obviously the catch consists of larger organisms. The material of 

 the tow-net is thus of necessity adapted to the nature of the 

 organisms which it is desired to catch. 



This is the instrument consecrated by long use, so that in 

 some quarters it is a heresy to suggest that it is, for the purposes 

 of modern investigations, rather an inefficient form of apparatus. 

 During the last few years, mainly under the stimulus of the 

 International Fishery Investigations, a number of new forms of 

 fishing apparatus, modifications of the older tow-net, have been 

 devised in NorAvay and Denmark and these have led to a great 

 extension of our knowledge of pelagic organisms of various kinds. 



The Heligoland young-fish trawl, to which, fortunately, the 

 name of a zoologist is not prefixed, is a bag of canvas, or some 

 other comparatively wide-meshed fabric, which is attached to a 

 square frame of metal tubing. The opening of this frame is 

 72 X 72 cm., and the length of the net is 3 metres. To the under 

 edge of the frame is the characteristic part of the apparatus, the 



Fig. 13. The Heligoland " Scberbrutnetz." (See Wiss. Meeresunt. 

 Kiel Komm. Abth. Helgoland, Bd. vi. Heft 1, 1904.) 



" sheering board." This is a square piece of galvanised iron plate 

 Avhich is hinged to the frame and is of the same dimensions. 

 It can be set at an angle to the frame, usually 125° inclining 



