CHAPTER VII. 



THE DISTRIBUTION OF THE PLANKTON. 



It is thus quite a practical proceeding so to employ quantita- 

 tive fishing apparatus as to obtain all the plankton organisms 

 which exceed a certain size, and which are contained in a column 

 of sea water of known dimensions and position. Further, it is 

 comparatively easy to count these organisms. The work is 

 laborious and monotonous but presents no inherent difficulties to 

 anyone familiar with the organisms captured. Then having made 

 such a catch and counted the individuals contained in it we are 

 justified in saying, for instance, that the Irish Sea 10 miles north 

 fi'om Llandudno contained on a certain date so many fish ova, so 

 many Noctilucae, so many copepods and so many diatoms (to take 

 only the more abundant organisms which would be found) ; and 

 that these numbers of organisms were found in the water beneath 

 one square metre of surface. No exception can be taken to such 

 a statement if it is founded on the results of an investigation 

 carefully candied out. 



But should we be justified in stating that the Irish Sea 10 

 miles from Llandudno over an area of ten square miles contained 

 these numbers of organisms underneath each square metre of 

 surface over this whole area, and that the aggregate number of 

 organisms could be calculated by simply multipljdng the numbers 

 of each species contained in the sample catch by the number of 

 times that one square metre was contained in the entire area ? If 

 we say that we can do so then we assume that the plankton is 

 uniformly distributed over the whole area referred to, and that it is 

 generally evenly spread over the sea throughout wide areas. Now 

 is this the case ? 



