PELAGIC FLOATING CRUSTACEA 139 



and the " drifters," or Plankton. The former include 

 the larger and more active animals, such as fish, 

 whales, and the like, whose movements are more or 

 less independent of the movements of the water; 

 the latter comprise the plant-life and the floating or 

 feebly swimming animals that drift at the mercy of 

 waves and currents. A great deal of attention has 

 ben given in recent years to the study of the 

 plankton, and it has come to be recognized as filling 

 a very important place in the balance of life in the 

 sea. In the sea, as on land, all the animals are 

 ultimately dependent on plants for their food. The 

 larger and more conspicuous sea-weeds which grow 

 on the sea-bottom, however, can only flourish in 

 comparatively shallow water, and the region which 

 they occupy forms only a narrow fringe round the 

 land-masses of the globe. It is only necessary to 

 look at a map of the world, showing the depth of 

 the sea, to realize what an insignificant part of the 

 area of the oceans contributes in this way to the 

 food-supply of marine animals. The microscopic 

 plant-life of the plankton, however, makes up for the 

 individual minuteness of its constituents by their 

 incalculable numbers. The lowly organisms known 

 as " diatoms," familiar to the microscopist from the 

 beauty of their flinty skeletons, are among the most 

 numerous and important of these, and they are 

 associated with a great variety of other single-celled 

 algae and allied organisms, some of them so minute 



