outer surface of the
dredge and the last few fathoms of dredge rope. In order to increase the
effectiveness of this method of capture a bar was fastened to the bottom
of the dredge, to which bunches of teased-out hemp were tied. In this
way specimens of the greatest interest, and frequently of equal
importance with those in the dredge bag, were obtained. The tangle bar
was at first attached to the back of the net. From the "Challenger"
expedition onward it has been fixed behind the net by iron bars
stretching back from the short sides of the dredge frame which pass
through eyes in their first ends (fig. 15). The swabs are thus unable to
fold over the mouth of the dredge. Rope lashings to the lips of the
dredge are sometimes added, and a weight is tied to the larger bar to
keep it down.

[Illustration: FIG. 15.--Deep-sea Dredge, with Tangle Bar.]

Occasionally the tangle bar is used alone (Agassiz), and one form
(Tanner) has two bars, stretching back like the side strokes of the
letter A from a strong steel spring in the form of an almost complete
circle. The whole is pulled forward from a spherical sinker fastened in
front of the spring apex; and should the apex enter a crevice between
rock masses, the side bars are closed by the pressure instead of
catching and bringing up. This is said to be a very useful instrument
among corals.

_The Blake Dredge._--In the soft ooze which forms the bottom of deep
seas the common dredge sinks and digs much too deeply for its ordinary
purpose, owing partly to its chief weight bearing on the frame only,
partly to its everted lips. To obviate these defects Lieutenant
Commander Sigsbee of the "Blake" devised the Blake dredge. Its novel
features were the frame and lips. The former was in the form of a
skeleton box; that is, a rectangle of iron bars was placed at the back
as well as the front or mouth of the net and four more iron bars
connected the two rectangles. The lips instead of being everted were
in parallel planes--those, namely, of the top and bottom of the net.
The effect of this was to minimize digging and somewhat spread the
incidences of the weight. Another advantage was that the net being
constantly distended by its frame, and, moreover, protected top and
bottom by an external shield of canvas, quite delicate specimens
reached the surface uninjured. The dredge weighed 80 lb. and was 4
ft. square and 9 in. deep.

_Rake Dredges._--These a