184 Marsh—Limnetic Crustacea of Green Lake. 
XIII.) fifteen centimeters long, by five centimeters broad. The 
frame is strengthened by three transverse braces. The frame 
and braces are made of strips cut from sheet brass, one milli¬ 
meter thick and two centimeters wide. 
Through the horizontal pieces of the apparatus are drilled 
two holes large enough so that the heavy brass wire D E will 
slide easily up and down. To the middle of this wire at E is 
attached an upright piece which passes through the lower part 
of the frame B, and strikes against the brace C. The wire is 
held in place by a rubber band passing around the plate B. 
The dredge is hun g from this central pin at E, and cannot be 
detached exce pt as the wire D E is lowered so as to throw the 
ring off the pin. 
The releasing apparatus is fastened to the dredge rope by 
copper wire passed through small holes drilled in the upper and 
lower plates. The messenger is a brass cylinder five centi¬ 
meters long and four centimeters in diameter. 
The work of dredging is done from a row boat which is fitted 
with a sail. The mast is unshipped, and in the mast hole is in¬ 
serted an upright about six feet long, to which is attached 
a cross piece extendin g over the side of the boat. Prom this 
cross piece the dredge is suspended by a pulley block, and upon 
the cross piece is a hook from which the messenger is suspended. 
The dredge is lowered vertically, and after being raised to the 
required point, is “set off” by the messenger. When the mes¬ 
senger strikes the releasing apparatus the top of the dredge 
falls over, and it remains suspended by the middle. At the 
same time the weight of the dead causes the cord around the 
middle of the dredge to tighten, so that there is a double safe¬ 
guard against the entrance of any other organisms —- the in¬ 
verted top and the stricture of the suspending cord. 
There is one sour ce of inaccuracy in this dredge, and that is 
the loss of material, when it is released, between the top and 
the cord passing around the center. My hauls, however, were 
made through five meter distances, and I do not think that in 
this distance, the loss would have much effect on the results, 
and, of course, for comparative work it need not be considered 
at all. 
