METHODS OF COLLECTING AND PHOTOGRAPHING 



73 



No. 5 spring brass wire, standard American gage, has three pairs 

 of wire rings h soldered on it at equal distances to hold the 

 drawlines dl in place. To the drawlines at 

 their junction a short cord wl may be attached 

 for the support of a weight. 



If the net is used in this form the catch 

 must be removed from it by turning it inside 

 out and sousing the tip in a bottle of water. 

 It is more convenient to cut off the tip of 

 the net along the line if and tie into it a 

 screw tip like that described below for the 

 cone dredge, but without the weight. A short 

 glass tube closed by a rubber stopper or a 

 bucket like that of the plankton net may be 

 used in place of the screw tip. Provided with 

 a bucket the net is identical with the plankton 

 net except that it lacks the canvas cone. 



The townet may be dragged behind a boat 

 either at the surface or submerged to any depth 

 by means of a weight attached to the weight 

 line. When the haul is completed the net is 

 soused in the water or water is thrown on its outer surface, until 

 the contents are washed to the tip of the net, which is then turned 

 inside out and the contents obtained by rinsing the tip in a bottle 

 of water, or allowing them to fall into preserving fluid. The pro- 

 cedure for a net provided with a bucket is described under the 

 plankton net and cone dredge. 



2. Plankton Cylinders. Various forms of apparatus have been 

 designed for collecting plankton from a rapidly moving boat. These 

 are made with a very small opening for the entrance of water and 

 with a large filtering surface. They are designed to reduce the 

 pressure of the water on the filtering surface. They are described 

 by Steuer and others. They are chiefly of use in the sea or in 

 other situations accessible only to large vessels and are little em- 

 ployed in fresh water. The plankton cylinder is one form of such 

 apparatus in which a torpedo-shaped metal jacket admits water 

 through a small opening on its conical end and carries the filtering 

 gauze in the interior or on its other end. 



FIG. 16. Showing method of 

 laying out a pattern for cut- 

 ting two townets from a 

 yard of cloth forty inches 

 wide, a-b, line along which 

 cloth is to be cut. c-d, the 

 two net patterns, e-f, seam 

 by which the bottom of the 

 net is closed if no bucket is 

 attached (see Fig. 15). g-h, 

 line of attachment of bucket. 

 i-j, line along which net is 

 cut off when bucket is used. 

 (After Kofoid.) 



