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DISCOVERY REPORTS 



Fig. II. Fine-meshed netting used in tow-net construction. 

 Nat. size, a, 7 mm. mesh; b, 4 mm. mesh. 



a circumference of 22 ft. to 2 ft. 3 in., where it joins the canvas cyHnder, 2 ft. long, for 

 attachment to the bucket. The front section, B, 61 ft. long, is of 7 mm. mesh (knot to 

 knot) netting^ (Fig. 11 a), and C is 

 13 ft. long, of 4 mm. mesh netting^ 

 (Fig. II b). As in the N 100 there 

 are three longitudinal ropes, and in 

 addition transverse ropes passing 

 round the net, one between the sec- 

 tions B and C and one in the middle 

 of C These were originally made of 

 log line to prevent any tendency to 

 twist and so bunch up the net ; but 

 it was found not to be strong enough 

 and was replaced by ordinary manila rope of 2 in. circumference. The bucket, like 

 the others, is described on page 191. The closing rope is similar to that of the N 100, 

 but 40 ft. long, 2| in. in circumference and fitted with a large lignum-vitae bull's-eye. 

 In practice this net was not used a great deal. When the larger, rarer and more active 

 pelagic organisms were required the N 450, next to be described, which has an opening 

 over five times in area that of the N 200, was used whenever possible. For collecting 

 large quantities of the smaller forms the TYF was found to be more efficient. 



N 450. This net, with an opening of 4I m. diameter, is, we believe, the largest tow- 

 net yet fished. Its function, as already indicated, is to capture the larger and more 

 active pelagic animals, particularly the deep-sea forms such as medusae, Crustacea, 

 cephalopods and fish. It was feared by some that the difficulties in handling so large a 

 net, especially from a vessel encumbered with much rigging, might prevent its frequent 

 use. These fears, however, proved to be groundless. 



That the resistance in towing so large a frame, and one stout enough to retain its 

 shape out of water, should be reduced to a minimum was here a matter of great im- 

 portance and, as in the N 200, a stream-line section of similar construction was adopted. 

 The details and dimensions are given in Fig. 12. To facilitate stowage the frame was 

 made in four sections to bolt together, and hinges were provided at two joints so that 

 if necessary it could be collapsed into two semi-circular halves for taking inboard. This 

 latter device, however, was found to be unnecessary and was never used. Despite its 

 great strength it was found that, when hoisted into the air by one point, it tended to 

 lose its circular shape ; this was prevented by the introduction of a thin steel wire across 

 the diameter of the ring from the point of suspension. As shown in Fig. 12 the bridles, 



1 To find a make of strong and fine netting suitable for these large plankton nets was a matter of con- 

 siderable difficulty. The two sorts of square-meshed netting shown in Fig. 11, which were also used for 

 fine nets attached to the trawl and for other purposes, were obtained from L. de Sereville, 3 Rue d'Haute- 

 ville, Paris X. The 4 mm. netting is supplied in widths of 2 m. 10 cm., and the 7 mm. in widths of 2 m. 

 50 cm. 



