524 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



which continued to raise water whilst the tube was either 

 lowered or raised. Since it is questionable whether this 

 method of sucking up the water would have an effect on 

 the catch, the entrance of the plankton and its passage 

 up a tube was observed by Lohmann by using a glass 

 tube. It was distinctly seen that the organisms in the 

 centre of the tube ascended more rapidly than those 

 against the walls. This difference in the current is, 

 however, of no importance for the equal raising of the 

 whole water column, because from each section the same 

 quantity of central and peripheral water will be taken up 

 respectively. It was noticed that some of the large 

 animals were sensitive to the streaming, and Copepods, 

 for example, moved energetically against the current. 

 If, therefore, the current is slow, it is possible for the 

 larger forms to move out of the tube, but, since the 

 average speed of the current is 57 cm. per second, this is 

 impossible; and any loss occurring when the pumping 

 method is used applies only to the destruction of fragile 

 forms in the nitration. 



The water must be filtered, either on the ship or 

 when conveyed back to the laboratory. The latter is 

 probably the more simple. The water is pumped into 

 large sulphuric acid " carboys " of about 28 litres con- 

 tents, and a \ litre of commercial formol is added so 

 that a 2 per cent, solution results, which suffices to kill 

 the organisms and to fix them. The filter is simply 

 hardened paper, which is folded into a cone and is held 

 in a zinc funnel of about 50 centimetres diameter at the 

 mouth. It is best to construct an arrangement so that 

 the water can run from the carboys into the filter at the 

 same speed as the latter filters. The whole can be then 

 left to run of its own accord, with but an occasional 

 glance to see that the filter does not become stopped. 



