Methods in Plankton Investigations. 15 



<b ' 



the connector. The cone is suspended from the top by means 

 of three stays (st.), and sheds the water centrifugally against 

 an inner net (/. n.) of No. 12 silk. This net is hung from a 

 ring (/-. /.) lixed to the under surface of the cover by three 

 supports, one of which (t. s.) swings upon the pivot (/>.) and 

 permits the removal of the net. The inner net conforms to the 

 proportions of the outer net but is only 27 cm. in diameter at 

 the top. At its apex is an opening 8 cm. in diameter, through 

 which plankton caught on the sides can be washed into the 

 lower part of the outer net. 



To secure rigidity the margin of the cover is provided with a 

 projecting horizontal wing (ti'.), to which is attached the foot 

 (Plate IV., Fig. 8-10,"/.). This in cross-section is L-shaped, 

 extending obliquely downward and outward, the oblique and 

 horizontal arms being respectively 2.5 and .75 cm. in length. 

 The foot fits into a circular trough (/;-.) 1-1.25 cm. in width 

 and 2.75 in height. The inner wall (Fig. 9, 10, i. w.) of the 

 trough is parallel to the oblique face of the foot, against which 

 it rests when the cover is in place. The cover is held in the 

 trough by means of four turn clamps (Fig. 9, c), which are 

 fastened by straps (str.) upon the outer wall (o. w.) of the 

 trough. When the clamps are released and swing to the posi- 

 tion c-', the cover can be removed, and the upper margin of the 

 outer net (Fig. 9, o. n.) can be folded over the inner wall of 

 the trough. When, now, the cover is replaced, the net is 

 firmly clamped between the oblique face of the foot and the 

 inner wall of the trough. (Cf. Fig. 9 and 10.) This method 

 of attachment permits the ready removal of the net for the 

 purpose of drying the silk, and at the same time insures a 

 tight joint. 



The net is made of the customary No. 20 silk and meas- 

 ures 92 cm. on the side. The upper border is faced upon 

 the outer surface for cm. and upon the inner for 2 cm. 

 with butchers' linen, so that the wear in the fastening of 

 the net falls upon the linen, while the silk only is exposed to 

 the water to be filtered (Fig. 10). To insure the uniform 

 placing of the margin of the net in the fastening, a heavy cord 

 (at.) is sewed in the border, against which the angle of the foot 



