240 THE DEPTHS OF THE SEA. [cuar. 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, but philosophers using it in deep water 
very generally found that 
whether from clumsiness 
or from want of sufficient 
4 practice, they had got the 
7 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 
VOT \ things scarcely visible to 
; ae WEN 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 
SOOOTRO S41 1 
i 
Fig. 45.—‘ Ball's Dredge.’ 
