VARIOUS SOFT-BODIED INVERTEBRATE ANIMALS. 99 
the "Bulletin of the U.S. Nat. Museum," 1892, Vol. XXXIX., 
Pt. G, pp. 26-30. If a ready-made naturalist's dredge has not 
been obtained, the apparatus can be made by a blacksmith. A 
good average size for moderate depths is 20 inches by 5 for the 
frame, and 2 feet length for the net. Dall recommends that a 
frame of galvanized iron should be riveted on near the back 
edge of the iron frame, and the canvas and net laced with copper 
wire into holes in the galvanized iron ; thereby the bad effects of 
iron rust on the net are avoided. The upper and lower outer edges 
of the frame are bevelled to enable the dredge to catch along the 
bottom. The rope is attached to the ring of only one of the arms, 
the two arms being fastened with cord. The object of this is to 
lessen the risk of losing the dredge if it gets fixed among rocks ; when 
this happens the cord breaks, thus allowing the arms to separate 
and the dredge to be released. It may be necessary to fix a weight 
on the rope about 10 feet from the mouth of the dredge, in order 
to keep the edge of the frame along the bottom. The length of rope 
required for small depths is equal to about twice the depth. The 
feel of the rope is the best indication as to how the dredge is working. 
When the dredge is hauled up, delicate specimens should be 
picked out before disturbing the contents. To separate specimens 
from the mud and fine sand, place the dredged material in a sieve 
and rotate it in a tub of water. Any very small specimens that pass 
through the sieve can be secured later by gently stirring up the mud, 
pouring off the liquid, and adding more water. After this process 
has been repeated a few times, the mud becomes washed away, and 
the specimens will then be seen lying at the bottom. 
A tangle is useful for catching up spiny specimens. The apparatus 
consists of an iron bar, straight or bent at a right angle, and with 
five or six pieces of chain attached to it. Untwisted strands of rope 
are attached to the chain-links. 
Towing-net. — A towing-net is used for surface or pelagic animals. 
A conical net of cheese-cloth, bolting-cloth, or coarse- woven bunting, 
about 2| feet in length, is fastened to a copper ring about 1^ feet in 
diameter ; it is best to double a strip of cotton cloth round the ring, 
and sew the net on to the cotton. Four equal lengths of strong fine 
cord are fastened at equidistant points round the ring, and tied 
