Methods in Plankton Investigations. 5 



6 ' 



If, now, we complete the truncated cone and denote the side 

 of the small cone, added for completion, by x, it follows that 



x : x-\-i : : r : R; 



x = -j; — = 7.619 cm. 

 K—r 



If, now, we imagine the surface of the completed cone 



unrolled and spread in one plane (Fig. B), the circumferences 



C ( = 2 R n ) and c ( = - 2 r n ) will form arcs subtending an 



unknown angle or, and it follows that the circle described by 



the radius x ( = = %xn ) is to 2 r n as 360° is to a, or 



2x7i 360 



2 r 7T a 



360 r 



a = ; 



x 

 a= 94.5°. 



This angle a being known, it is a simple matter to lay off 

 the pattern for the net. The pattern for the linen head-piece 

 is constructed in a similar manner. Allowance must be made 

 along the edges mr and ns (Fig. B) for the longitudinal seam. 

 It has been our custom to allow 4 mm. upon one margin and 

 8 mm. upon the other (Fig. 2, Plate I.). The two edges are 

 brought together and backstitched at a (Fig. 2), and the wider 

 margin is then turned under the other and felled at b upon 

 the outside of the net. Thus only a single seam 4 mm. in 

 width traverses the length of the net. A very fine needle is 

 used in the sewing, and the line of stitches can be effectually 

 closed with a light coat of rubber cement. Allowance must 

 also be made along the edge mn for attachment of the silk 

 between the linen cone (Plate I., Fig. \,c. b. I.) and the cover- 

 strip (e. s.) at the seam sm, and for the fastening of the silk, 

 along the margin rs, between the net clamp (n. e.) and the 

 head-piece {h. p.) of the bucket. In order to get the net into 

 the clamp it is necessary to slit the silk at several points to 

 within a short distance of the line rs (Fig. B). 



b. The detachable bucket (Plate II., Fig. 3-5) used by us 

 differs in several particulars from that described by Apstein 

 ('91, '92, and '96) and also from the one devised by Reighard 

 ('94, p. 26, Plate II.). It copies the Reighard bucket in sub- 



