PLANKTON 



233 



column of water and give a catch 

 which, when multiplied by a co- 

 efficient, would be the exact con- 

 tents of so many fathoms of, say, 

 a square metre in section — a 

 most desirable result, if possible 

 of attainment. Moreover, the 

 Kiel planktologists assumed a 

 uniform distribution of the or- 

 ganisms in sea areas under con- 

 stant conditions ; and by these 

 methods arrived at far-reaching 

 conclusions in regard to the 

 amount of food matters in the 

 sea, such as the numbers of 

 floating fish- eggs and of the fish- 

 populations — all based upon (1) 

 the supposed uniform distribu- 

 tion over wide areas and (2) the 

 vaHdity of a comparatively 

 small number of samples taken 

 at considerable distances apart. 

 Fig. 3, on Plate XVIII, shows 

 one form of the Hensen quanti- 

 tative net. 



Before considering these and 

 other quantitative methods more 

 in detail, it may be convenient to 

 name and characterize briefly a 

 few of the leading groups of the 

 plankton and some represen- 

 tative genera which may re- 



FiG. 16. — "Nansen" Closing Tow-Net in Action. 



I. Open, as it descends and as it fishes coming up. 



II. Closed, as it is when hauled in after fishing. B, brass bucket containing 

 the catch. C, canvas front to net. L, releasing apparatus. M, brass mes- 

 senger sent down line to effect closing. T,the throttling noose. W, weight. 



