THE IMPENETRABLE SEA 



cilia, which have all the characteristics of protozoa) ful- 

 filling various purposes as parts of organs belonging to 

 them, they live at the expense of other living animals. 



As an instance of this ''independent parasitism" we 

 have the free-swimming flagellates of the sea. 



Chief among ocean plants are the diatoms, which 

 comprise more than half the oceanic plants, and are 

 microscopic plants of the group Diatomacea, with cells 

 composed of two symmetrical valves. They multiply 

 by spontaneous separation. There are more than four 

 thousand species of these tiny plants, scattered over the 

 waters of the world, and their structures show an infinite 

 variety of designs of great beauty, rivalling the diversity 

 and perfection of snow crystals. Besides the diatoms there 

 are certain species of blue-green algae and the flagellates, 

 which compensate to some extent for their dependent and 

 independent parasitism by manufacturing vegetable food 

 in the sea. But when they exhibit malevolent qualities 

 they can foul the waters so badly that they poison large 

 numbers of fish. 



They caused what was termed the ''Red Tide" that 

 washed the shores of Florida in 1947 and killed — it was 

 estimated — over fifty million fishes, large numbers of 

 which were washed up on the shores in such states of 

 decomposition that they stank disgustingly. So thickly 

 did they swarm in the sea on that occasion that a single 

 pint of sea water was found to contain over sixty million 

 flagellates. 



The free-swimming flagellates of the ocean, therefore, 

 present us with the paradox, that they can be enormously 

 beneficial to ocean life, as creatures which are half plant, 

 half animal, manufacturing protoplasm as the life-giving 

 substance upon which myriads of fishes and other sea 

 animals feed; and they can be life-destroyers when, by 

 an excess of breeding, they poison vast numbers of other 

 creatures of the sea. 



All those forms of Protozoa classed as flagellata — 



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