522 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



catches made by the apparatus to be described below, it 

 has been found that the Metazoa, with few exceptions, 



are completely or sufficiently caught by the plankton net, 

 whilst of the Protozoa only a few large forms, Noctiluea, 

 Ceratium tripos, &c, or species with long spines, will be 

 obtained. In fact, the number of individuals present in 

 the sea is from 5 to 100 times greater than is demonstrated 

 by the net, and the species which form this loss are not of 

 "no importance," but are the chief forms of food for the 

 larger species, and therefore of great significance in the 

 metabolism or see-saw of life in the ocean. If, there- 

 fore, the Metazoa or larger Protozoa and Protophyta only 

 are to be studied, the net can be used as the best instru- 

 ment by far for the capture, whether for quantitative 

 or qualitative purposes. If a complete investigation of 

 the plankton is to be made, and the relation of larvae to 

 adults and food to the eaters of it are to be considered, 

 other kinds of apparatus must be used. Of these, the 

 most important is the Pump and Tube, by wdiich water 

 is pumped up to the boat and later is filtered. In shallow 

 water, and up to 100 metres deep, the net can be more or 

 less supplanted by the pumping method, but, unfortu- 

 nately, for greater depths, and for regions where there are 

 strong currents, the pumping method is hardly applicable. 



Pump, Tube, and Filter Method. 



Essentially the method consists in the pumping up 

 of a vertical column of water, which is filtered on the 

 vessel or, later, on shore. An indiarubber tube of 

 sufficient length for the deepest regions is required, and 

 this is lowered vertically in the water by means of a 

 rope attached to the lower end, and in the same way is 

 slowly pulled up, whilst at the same time the water is 

 pumped out of the upper end by a small brass pump. 



