GERMAN PLANKTON INVESTIGATIONS. 337 



There are two rows of metal rods, winch serve to keep 

 the net in place. The inner row, not visible in Fig. 11, is 

 attached to the lower metal ring R' . This row of rods is 

 external to the net. The outer row attached to the ring 

 R is inside the net, and serves to keep its folds in position. 

 When the headpiece, H, is taken off from the metal cover- 

 ing, W, it is possible to remove the upper ring R with the 

 attached rods, which lie, as has been noted above, outside 

 the net. The net itself can be subsequently removed, 

 inverted, its contents washed out, and it can then be 

 replaced in the metal covering. 



Attached to the upper end of this covering are three 

 metal rings. To the ring X a weight of about half-a- 

 hundredweight is attached, the use of which is indicated 

 below. To the ring Y, and to a similar ring 180° away 

 from it, ropes are attached which allow of the net being 

 let out and hauled in. The cover is fastened to the 

 cylinder by means of three overfall screws, two of which, 

 S and S', are shown in the figure. 



In the cover H of the cylinder there is a turbine to 

 which an indicator is attached, by means of which the 

 volume of the inflowing water can be estimated. The 

 turbine is mounted on an axis provided with stones, the 

 points on which the turbine rotates are of Iridium-plati- 

 num. Iron is useless for the purpose, as it so soon 

 becomes rusty. It does not much matter if a little water 

 flows into the net near the turbine, that is, where the 

 turbine rotates, but it is better to avoid this loss. In the 

 tube of the turbine there is, therefore, a sharp cutter 

 which prevents this, and also serves to cut to pieces any 

 organisms that might lodge there, and prevent the rota- 

 tion of the turbine. On the axis of the turbine an indi- 

 cator is placed. This measures up to 15,000 revolutions. 

 When the turbine has revolved 1,400 times about 500 

 x 



