240 



THE DEPTHS OF THE SEA. 



[CHAP. vi. 



suitable for scientific purposes. The oyster dredge 

 has a scraper only on one side. In the skilled hands 

 of the fishermen this is no disadvantage, for it is 

 always sent down in such a way that it falls face 

 foremost, hut philosophers using it in deep water 



very generally found that 

 whether from clumsiness 

 or from want of sufficient 

 practice, they had got the 

 dredge down on its back, 

 and of course it came 

 up empty. Again, oyster 

 dredgers are only allowed 

 to take oysters of a certain 

 size, and the meshing of 

 the commercial dredge is 

 so contrived as to allow 

 all bodies under a certain 

 considerable size to pass 

 through. This defeats the 

 object of the naturalist ; 

 for some of the prizes 

 to which he attaches the 

 highest value are mites of 

 things scarcely visible to 

 the unaided eye. 



The remedy for these de- 

 fects is to have a scraper 

 on each side, with the arms attached in such a way 

 that one or other of the scrapers must reach the 

 ground in whatever position the dredge may fall ; and 

 to have the bag deeper in proportion to the size of 

 the frame, and of a material which is only sufficiently 



FIG. 45.' Ball's Dredge.' 



