262 



THE SEAS 



dredge " (Fig. 54). This varies in dimensions according 

 to the size of the ship from which it is to be used, but in 

 essentials it consists of a rectangular or triangular shaped 

 frame of iron to which is attached a short bag of strong 

 netting. The mesh of the net depends on the size of the 

 animals that are to be caught. The frame at the mouth 

 of the net has sharp bevelled edges which can dig through 

 the sand and gravel, and will scrape off any animals that 

 are fixed tight to the rocks. This net is used for all sluggish 

 bottom animals such as starfish, shellfish and sea urchins, 

 and also for those animals that burrow in the surface 

 layers of the sand or mud. 





Fig. 54. — A naturalist's dredge. 



For the swimming animals nets similar to those used by 

 fishermen are employed. These, consisting of trawls, 

 drift nets and seines, will be described in detail in the 

 chapter on the sea -fisheries. In addition a small net 

 known as the Agassiz trawl, named after its inventor, 

 is used for deep-sea work (Plate 94). This net has the 

 advantage that whichever way it may fall on the sea 

 bottom it can still fish effectively, a very important point 

 when fishing in great depths, as it is impossible to ensure 

 that the net may not turn over several times in its long 

 journey to the bottom. 



