42 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



arrived at very different conclusions as to the constitution 

 of the Plankton in that part of the ocean. 



It is possible to obtain a great deal of interesting 

 information in regard to the " hylokinesis " (or changes of 

 matter) of the sea without attempting a numerical 

 accuracy which is not yet attainable. The details of 

 measurement of catches and of computations of organisms 

 become useless, and the exact figures are non-significant, 

 if the hauls from which they are derived are not really 

 comparable with one another and the samples obtained are 

 not adequately representative of nature. If the stations 

 are so far apart and the dates are so distant that the 

 samples represent little more than themselves, if the 

 observations are liable to be affected by any incidental 

 factor which does not apply to the entire area, then the 

 results may be so erroneous as to be useless, or worse than 

 useless, since they may lead to deceptive conclusions. It 

 is obvious that we must make an intensive study of small 

 areas before we draw conclusions in regard to relatively 

 large regions such as the North Sea or the Atlantic Ocean. 

 That, however, is not an argument against the 

 legitimate use of quantitative methods, with limitations, 

 and for certain purposes. It is necessary to know more 

 than the fact that a certain species is present at a given 

 locality at a certain time. We must endeavour to get 

 some measure of its abundance, and that can only be done 

 satisfactorily by counting individuals; at the same time 

 recognising the imperfections of the methods and the 

 approximate nature of the result, so that the numerical 

 estimate will be regarded as relative rather than absolute. 

 Our apparatus is not perfect enough, nor is the distribu- 

 tion of the organisms sufficiently uniform to enable us to 

 calculate how many individuals of a Diatom, of a 

 Copepod, or of a fish are present in the Irish Sea on a 



