506 TRANSACTIONS LIVERPOOL BIOLOGICAL "SOCIETY. 



net. It can be described therefore as the filtering bucket. 

 It consists of a 14 cm. long brass cylinder, whose sides 

 are cut out, with the exception of three narrow pieces, 

 so that there remains o cm. of cylinder above ami 1 cm. 

 below. A piece of No. 20 silk is then placed outside the 4 

 three brass pieces and fixed above and below to the 

 cylinder by the clamp rings. In addition, three brass plates 

 are screwed against the pieces so that the silk filtering 

 tissue lies between them and is quite taut over the three 

 windows of the bucket. The upper part of the cylinder is 

 supplied with a screw thread so that it can be screwed on 

 to the brass ring, to which the net is attached. From the 

 middle of the floor of the cylinder a tube descends, which 

 is provided with a tap. 



This completes the description of the ordinary Apstein 

 net, but in order to make comparisons of the various 

 layers, and the plankton at different depths (a most 

 important factor, for it will be shown that the plankton 

 differs both quantitatively and qualitatively considerably 

 according to the depth and probably as a result of changes 

 in the light conditions, salt contents or temperature), it is 

 necessary to have a method by which the net can be 

 hauled through a certain distance and then closed. In 

 fact, when working with the vertical net, the column 

 from the bottom to the surface should be divided into 

 regions, and the temperature, and salt contents, together 

 with the plankton, determined for each region separately. 

 Various arrangements have been invented for closing the 

 net. The following is about the most satisfactory now 

 in use (fig. 3). The net differs from the one just 

 described only in the possession of closing apparatus. 

 The upper brass ring of the conical mouth-piece is 

 replaced here by a much broader and heavier brass ring. 

 Across the middle of this runs a stout bar, and directly 



