Method of Using the Dredge. 
429 
(2) It is operated by weights, which work positively, and 
does not depend upon springs or wheels, whose action is more 
or less uncertain. 
(3) It is tight, so far as the Crustacea are concerned. The 
coarseness of the wire mesh of our bucket does not permit us to 
assert that it is equally tight to Peridinium and similar minute 
creatures. It would not be difficult, however, to construct a dredge 
on a similar pattern whose cover should be entirely secure 
against the entrance of any organisms when the dredge is 
closed. 
As disadvantages of the dredge may be mentioned: 
(1) The amount of the weights required for working the cover. 
This, however, is not much greater than is necessary to cause 
the dredge to sink promptly and rapidly through the water. 
(2) The resistance offered by the cover in drawing up the 
dredge, and the time required by the messengers in descending 
to open and close it. These are, however, of comparatively 
slight moment in water so shallow as ours. 
(3) A more important objection lies in the fact that the 
dredge must be used as a vertical dredge only. The boat 
from which it is worked must be practically stationary, and 
preferably should be anchored. If the boat is drifting through 
the water, the pressure of the water on the cover of the dredge 
so hinders its sliding that a weight which works it perfectly 
when the dredge is vertically suspended fails to open or close it. 
Further, if the dredge line is not vertical, a messenger which 
ordinarily is amply heavy for releasing the weights may fail to 
sufficiently depress the weight-pin. 
METHOD OF USING THE DREDGE. 
The mode of working the dredge is as follows: The dredge is 
hung to the dredge line, and the opening and closing weights 
are hung to their respective supports. The weight-holders are 
hung to the pins of the release - , so that the weights are sup¬ 
ported by the release cords. The cover is slid into place, and 
the dredge lowered. When it has reached the proper depth the 
smaller or opening messenger is sent down the line. It strikes 
and depresses the short fork, releases the opening weight, which, 
