1^11] Kofoid: Self-closing PJaukton Net. 321 



the filtering area of the sill? bag normally exceeds the area of 

 the orifice of the net and the upper cone of the net is of im- 

 pervions canvas, there is no certainty that the irregularities in 

 movement of the net after closure will not open the lids, spill 

 out part of the catch, or even admit other organisms. This 

 type of closing-net seems to have been first figured by Apstein 

 (1906). 



Fowler's (1898) "inid-water" tow-net is devised for vertical 

 work, is sent down closed, and is opened and closed again by 

 messengers. The net is suspended by two sets of chains to the 

 "locking gear" or tripping apparatus at the end of the cable. 

 The mouth of the net is rectangular with hinged .jaws working 

 on a central axis. When suspended by the closing chains the 

 two jaws are held together by weight of the net, when suspended 

 by the towing chains the jaws fall open by their own weight 

 and the tension upon the net. This net was used extensively 

 by Fowler in his investigations in the Faeroe Channel and Bay 

 of Biscay and worked satisfactorily. It was also used on the 

 "Valdivia" and "Siboga" expeditions (see Fowler, 1898, and 

 Weber, 1902). The criticisms which might be passed upon it 

 are perhaps more of a theoretical than of a practical nature. 

 The large tripping apparatus and the bar and chains across 

 the opening are undesirable as impeding the entrance of active 

 or filamentous organisms. It also seems to the writer that the 

 light weight of the net, upon which the certainty and continuity 

 of closure wholly rest, is its weak point. The frame weighs, 

 according to Fowler, only sixteen and one-half pounds and this 

 would be reduced in sea-water to about fourteen pounds. The 

 locking gear and chains weigh thirty-three pounds and have less 

 area of resistance than the net and bag. It would seem possible 

 that the surge of the ship and irregularities in heaving in the 

 cable might lead to an intermittent gaping of the jaws of the 

 net before opening or after closing, since the heavier locking 

 gear would tend to respond more readily than the lighter net 

 and bag to oscillations of the cable. With an even tension on 

 the towing chains there is no chance for the resistance of filtra- 

 tion to spread the jaws, but the instant the chains are slackened 

 their weight at the ends of the closing levers would tend to open 



