I] 



THE CATEGORIES OF LIFE 



25 



These latter creatures are far more important 

 from the point of view of the economy of the sea 

 than are the larvae. They constitute probably the 



Fig. 4. Plankton: Unicellular organisms. 1, 2, 3, 7, 10, 11, 12, 13, 

 16, 17, 18, Diatoms; 4, 5, 6, 9, Peridinians; 8, an Algal repro- 

 ductive Cell, or Zoospore ; 14, Noctiluca ; 15, a Radiolarian. All 

 magnified. 



largest of all the categories of life in the sea, for 

 though they are very minute in point of size, yet 



