232 TRANSACTIONS LlVERPOOl BfOLOGICAL SOCIETY. 



fauna of the upper zones of the sea obtained by means of 

 the surface and Weighted open tow-nets. 



In many of these hauls during April (see Form 10, 

 p. 211) the vertical nets, although fchey had traversed a 

 very much smaller area of water, brought up a very much 

 larger number of Diatoms, for example in the case of 

 Chaetoceros contortum Id, 000, 000 in the Nansen and 

 280,000 in the Hensen, as against 160,000 in the weight 

 net and smaller numbers in those at the surface. Other 

 cases may not be so striking as this one, but still it is true 

 of many hauls that the Nansen net, especially, brought a 

 large number of Diatoms from the lower zone of water. 



In cases where, as on Form 71, p. 201, the Hensen 

 and Nansen nets have yielded smaller numbers, say. of 

 Copepoda than the weighted and surface nets no conclu- 

 sions can be drawn, as it must always be remembered 

 that the open tow-nets have sampled very much larger 

 volumes of water than have passed through the vertical 

 nets. Form 21, p. 209, shows a case where the Nansen net, 

 as usual, has caught much more than the Hensen, but 

 where it has not caught more than the average of the 

 three open tow-nets in the water above, but still when the 

 constitution of the catch is analysed it is noted that most 

 of the Diatoms are in the Nansen and Hensen nets, and 

 that the greater bulk of the catches from the upper layers 

 of water is made up of Copepoda and other larger 

 organisms. 



It is rare for the Hensen net to catch more than the 

 Nansen, but an example of that is seen on Form 45. p. 218. 

 The slight difference in bulk (0'5 c.c.) is, however, 

 probably due in this case to the presence of a few 

 Copepoda, Medusae and Oikopleura, and is thus of an 

 accidental or non-significant nature. Form 41 on p. 221 

 shows what we consider to be a fairly representative series 



