GERMAN PLANKTON INVESTIGATIONS. 



285 



of the network cannot become displaced, and the areas of 

 the meshes are, as a rule, very similar. As a rule the 

 mesh numbered 20 has been used, and for this number and 

 5 the number of meshes per square centimetre and the 

 length of a side of a single mesh are given. For number 

 5 each square centimetre has on the average 763 meshes, 

 and the length of each mesh is 0*2 mm. In number 20 

 the number of meshes is 5,926 and the length of side 

 0'05 mm. With the latter mesh most of the Diatoms 

 would be captured, though it would occasionally happen, 

 when they approached the mesh in the direction of their 

 longitudinal axis, that they slipped through. 



The silk bolting cloth must be so arranged between the 

 two rings that it cannot become folded. It is advisable in 

 the first place to cut out a paper pattern, the silk cloth can 

 then be cut accordingly. The net should have the form 

 of a truncated cone (Fig. 2). 



Fig. 



Let E and r be the radii of the larger and smaller rings 

 respectively, and let y be the height of the covering; let 

 x be the length of the truncated portion. These are the 

 dimensions chosen for the particular net. It is necessary 



