THE TEEMING LIFE OF THE WATERS 



geometrical in shape, which is composed of proteins 

 combined in the case of the Diatoms with silica, and 

 in the Dinoflagellates with pure cellulose. The latter 

 occupy an ambiguous position among lower creatures, 

 for, while their chlorophyll and cellulose suggest a 

 similarity to plant life, their possession of movable 

 filaments, which they move in the water like whips, 

 suggests a relation to the animal kingdom. 



This vegetable 



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plankton, this Phyto- 

 plankton, to give it 

 its proper name, be- 

 cause of its uniformly 

 simple structure and 

 minute size, stands 

 in very definite 

 contradistinction to 

 the animal plank- 

 ton, or Zooplankton, 

 which is much more 

 abundant and more 

 varied. If plants, by 

 their mass, outweigh 

 animals as inhabi- 

 tants of the land, 

 the animals have the 

 advantage in the 

 world of waters. Not only do the floating creatures 

 include Protozoa, unicellular beings comparable to the 

 Protophytes as regards size and mode of life, but they 

 present us with representatives of many animal groups, 

 even the highest. The huge squids and many fishes, 

 even very large ones, like the sharks, belong to this 

 category, and also the great Cetaceans, whalebone 

 and sperm whales, grampuses and dolphins, for they 

 swim and float from birth to death and are stranded 

 only by accident. These giants of the animal world 

 are as much a part of the plankton as the smaller 



Fig. 3. — Floating larva of a snail-like 

 mollusc of the genus Rissoa, with its 

 little spiral shell, from each side of 

 which spread out the two broad fila- 

 mentous outgrowths which enable it 

 to float in the water and form part of 

 the plankton. Later, its shell grows 

 and becomes heavier, and it sinks to 

 the bottom where it develops into the 

 adult form. 



