546 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



observations are carried out simultaneously, with the 

 object of making a complete investigation of the whole 

 area. 



One of the most important questions is, naturally, 

 the condition of the plankton at different places in these 

 areas at the same time, and the variations during the 

 year. Since at the time that these plankton investigations 

 are carried out, the hydrographical conditions are also 

 very thoroughly observed, there is an excellent oppor- 

 tunity of comparing both. Unfortunately, so far as the 

 plankton research is concerned, the only result of these 

 voyages four times a year has been the publishing of a 

 great series of tables, which, for purposes of comparison, 

 are practically worthless, since only one country, 

 Germany, has used the counting method of Hensen. The 

 total failure of the ordinary methods of estimation has 

 already been discussed above, and it w r as then pointed out 

 that, if the problems are to be solved, the more scientific 

 method of counting the organisms must be adopted. 



The distribution of plankton and its relation to the 

 hydrographical conditions has, to a certain extent, been 

 worked out by Apstein and others for the Baltic and North 

 Sea, from the catches made on the quarterly expeditions, 

 for the stations belonging to the German section (15). It 

 has been found of very great importance to use the closing 

 net, and, in addition to a vertical haul from the bottom 

 to the surface, to divide this column up into sections, as, 

 for example, where the depth is 210 metres, a haul is 

 taken from 210 to 65 metres, another from 65 to 25 metres, 

 from 25 to 5, and, lastly, from 5 metres deep to the 

 surface. This last catch is particularly important and 

 very often differs markedly in its constitution and volume 

 from the others. In all probability the surface layer of 

 water to a depth of only one metre is the layer concerned, 



