320 University of California Puhlications in Zoology. [Vol.8 



inward again and thus closes the net. This net is simple, with 

 an opening free from impeding bars, and the plan seems to be 

 capable of adaptation to deep-sea work, by the addition of an 

 automatic lock to hold the net firmly in place when closed and 

 by the necessary strengthening of the frame to carry the weights 

 needed below the mouth of the net. It would also need some 

 adjustment of parts at the rim to make the closure absolutely 

 complete and a supporting rod for the bag of the net to keep 

 it from wrapping itself about trips and cable during descent. 

 The general design is one meriting perfection and wider adoption. 



In his investigations upon the plankton of Bodensee, Hofer 

 (1896) used the horizontal net of the Cori (1897) model, which 

 he states functioned with extraordinary certainty, the opening 

 and closing of the net being distinctly noticeable on the cable, 

 even when the net was at the depth of one hundred meters. 

 He also adopted a net of the strangulation type towed by two 

 ropes, the tow-line passing obliquely to the net and a second 

 closing line vertically from the net to a life-preserver towed 

 sixty meters behind the boat. This method is criticized by him 

 as cumbersome. 



Marsh's (1897) vertical closing-net is lowered open, closed 

 by a messenger which releases the line which goes from the head 

 of the crowfoot to the trip, and transfers the weight of the net 

 to a constricting line about the middle of the bag. The upper 

 part falls down and effectively prevents the entrance of any 

 material during ascent after closure. The objections to this and 

 all other nets of its pattern are (1) that it is lowered open and 

 critical results are not obtainable since contamination is possible, 

 as a result of the swirl about the open mouth during descent; 

 and (2) the contents of the upper part of the bag where filtra- 

 tion is greatest may be lost in closing, a difficulty partially 

 obviated in the Nansen net by an elongated non-filtering area at 

 the head of the bag. 



The Petersen (1898) closing-net is a modification of the 

 Hensen plankton net, the only change being the addition of 

 two hinged semicircular lids which are released by messenger 

 and fall into closing position by their own weight. The net is 

 lowered open and the lids are not locked after closing. Since 



