252 FOUNDERS OF OCEANOGRAPHY 



case a large proportion — from 60 per cent, to 22 out of 

 34— of the observed variations are outside the range of 

 error of the experiment. 



To the question, What light does a series of, say, six 

 successive hauls throw upon the validity of a single haul, 

 say, the first of the series ? the answer seems to be that as 

 regards mere size (volume) and general nature (such as 

 phyto-plankton, zoo-plankton, or mixed) of the catch the 

 series confirms the representative character of the single 

 haul in a general way and within limits. 



But if one next proceeds to deal quantitatively with the 

 groups and the individual species, it is found that the hauls 

 in a series may differ widely: up to fully 50 per cent, of 

 the variations from the mean of the series extend beyond 

 the range of error and are therefore not due to possible 

 imperfections in the experiment. Thus more than half the 

 differences between the hauls of a series remains unaccounted 

 for, and may naturally be interpreted as evidence of an 

 unequal distribution of the plankton in closely adjacent areas 

 of water or in the same area in successive periods of time. 



Whether the present methods of collecting and of estimat- 

 ing are sufficiently accurate to enable us to determine the 

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

 able to assign probable upper and lower limits to the number 

 of each organism per unit volume of water, may be doubtful, 

 but we may hope that improvements in method and 

 accumulation of evidence may in time enable us to make 

 some approximation to an estimate of the population of 

 various sea-areas. Other more refined methods of collecting 

 samples of the micro-plankton have been recently devised 

 such as the filtering and centrifuging (or other exhaustive 

 examination) of small measured quantities of water, or the 

 cultivation of every organism in a very small volume of 

 water. These methods have added much to our knowledge 

 of the minuter and more elusive forms — the " nanno- 

 plankton," but the drawback to all of them is that they 



