MARINE BIOLOGICAL STATION AT PORT ERIN. '29 



at the time of observation in a given sea area, and to 

 trace the changes of this Plankton both in space and time. 

 This was a sufficiently grand conception, and it has been 

 of great service to science by stimulating many workers 

 to further research. In order to obtain answers to the 

 problems before him, Hensen devised nets of the finest 

 silk of about 6,000 meshes in the square centimetre, to 

 be hauled up from the bottom to the surface, and having 

 their constants determined so that it was known what 

 volume of water passed through the. net under certain 

 conditions. (See figure of the silk on PI. IV., p. 36). 



Now, if this constancy of distribution postulated by 

 Hensen could be relied upon over considerable areas of 

 the sea, far-reaching conclusions, having important 

 bearings upon fisheries questions, might be arrived at; 

 and such have, in fact, been put forward by the Kiel 

 Planktologists and their followers, and have been quoted 

 on many occasions. 



Such generalisations are most attractive, and if it 

 can be established that they are based upon sufficiently 

 reliable data, their practical utility to man in connection 

 with sea-fishery legislation will be very great. But the 

 comparatively small number of the samples, and the 

 observed irregularity in the distribution of the Plankton, 

 such ;is the examples given for the Irish Sea in the lasl 

 I wo (if these Annual Reports, and over still wider areas 

 such as the North Sea, leave the impression that further 

 observations are required before such conclusions can be 

 accepted as established. 



Of the criticisms thai have appeared in Germany, in 



the United Slates and elsewhere, the two most funda- 

 mental are: (1) that the samples are inadequate; and 

 (2) that there is no such constancy and regularity in 



distribution as Hensen and some others liave supposed. 



