GERMAN PLANKTON INVESTIGATIONS. 



287 



(F), and a metal funnel (D), which fits exactly into the 

 filter. The catch is carefully filtered, and then the metal 

 funnel (D) is removed. On unscrewing the screw (s) the 

 brass rod (b) can be moved downwards, while the arms (a) 

 are moved upwards, and then the filter and glass plate can 

 be removed. The catch remains on the glass plate. 



Fig 4. 



The use of the vertical net at sea is attended with 

 many difficulties. In the first place the ship must be 

 brought to, and even then it is impossible that a large 

 ship can remain perfectly still during the time necessary 

 for lowering and hauling in the net. The strain on the 

 net while being lowered and drawn up is controlled by 

 means of the apparatus well known in dredging as an 



