174 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



amount of this inequality in the distribution, so as to be able 

 to put probable upper and lower limits to the number of each 

 organism per unit volume of water may be doubtful. But 

 even if the data are not yet sufficiently numerous and reliable, 

 we must still work on in the hope that improvements hi method 

 and accumulation of evidence may in time enable us to make 

 some approximation to an estimate of the population of various 

 sea- areas. 



I would go further and say that even if we had no hope of 

 attaining to greater accuracy , our present planktonic results are of 

 some value. Although estimates which may be 25 or even 50 per 

 cent, wrong in either direction may not justify us in calculating 

 exactly the number of organisms and of potential food present 

 per area or volume of water, they do give us a useful approxi- 

 mation. Even if 100 per cent, out, doubling or halving the 

 estimated number is a relatively small variation compared with 

 the much larger increases and reductions amounting to, it may 

 be, ten thousand times in the case of Diatoms, ten to fifty times 

 in Dinoflagellates and five to twenty times in Copepoda, which 

 we find between adjacent months, and even greater differences 

 if we take groups of months, in a survey of the seasonal 

 variations of the plankton in European seas. 



