the position of this ground rope and
the greater size of the mouth. The absence of a lip makes it less
effective for burrowing and sessile creatures, but the weighted ground
rope nevertheless secures them to a very surprising extent. The
position of the ground rope is an important feature, as any free
swimming creature not disturbed until the arrival of the ground rope
cannot escape by simply rising or "striking" up. This and the greater
spread make the trawl especially suitable for the collection of fishes
and other swiftly moving animals. The first haul of the "Challenger"
trawl brought up fishes, and most of our knowledge of fish of the
greatest depths is due to it.

A tendency to return to the use of the small beam trawl for deep-sea
work has lately shown itself. That used by Tanner on the "Albatross"
has runners more heart-shaped than the "Challenger's" instrument; the
net is fastened to the downward and backward sloping edge of the
runner as well as to the beam, being thus fixed on three sides instead
of one; and a Norwegian glass float is fastened in a network cover to
that part of the net which is above and in front of the ground rope in
use, to assist in keeping the opening clear. These floats can stand
the pressure at great depths, and do not become waterlogged as do cork
floats. The largest "Albatross" trawl has a beam 11 ft. long, runners
2 ft. 5 in. high, and its frame weighs 275 lb.

_Agassiz or Blake Trawl._--This is generally considered to possess
advantages over the preceding, and is decidedly better for those not
experts in trawling. Its frame (fig. 18) consists of two iron runners
each the shape of a capital letter D, joined by iron rods or pipes
which connect the middle of each stroke with the corresponding point
on the other letter. The net is a tapering one, its mouth being a
strong rope bound with finer rope for protection till the whole
reaches a thickness of some 2 in. It is fastened to the frame at four
points only, the ends of the curved rods, and thus has a rectangular
opening.

[Illustration: From Alexander E. Agassiz's _Three Cruises of the
"Blake."_ By permission of Houghton, Mifflin & Co.

FIG. 18.--Agassiz or Blake Trawl.]

The chief advantage of this frame is that it does not matter in the
least which side lands first on the bottom; it is to the other trawls
what Ball's dredge is to an oyster dredge. The cou