THE IMPENETRABLE SEA 



The word ''plankton" does not merely mean "wander- 

 ing", as it is usually translated, for the word has a dis- 

 tinctly passive sense, suggesting ''that which is made to 

 wander and drift". It therefore does not merely define 

 the tiny creatures which form its greatest bulk, but all 

 those creatures of the sea which float and drift with its 

 tides and ocean currents (the animals and plants which 

 are passively carried about) in contrast to whales and fish 

 which swim and move at will through the waters. This 

 means that the babies of all kinds of fish must be classed 

 as plankton, if they are small enough to be borne help- 

 lessly along by the sea. 



Tunny fishes consume large quantities of plankton, 

 being quite indiscriminate regarding the nature of it, 

 while flying-fishes also consume countless millions of 

 planktonic creatures, particularly Copepoda. 



These copepods constitute the large order of minute 

 crustaceans (found in both salt and fresh water) which, 

 by their abundance, provide food for all kinds of larger 

 sea creatures. In typical copepods (the name means 

 "oar-feet") the body is distinctly segmented, the abdo- 

 men is limbless, and the thorax bears four or five pairs 

 of branched appendages. All of the tiny creatures are 

 one-eyed. The appendages are truly oars rather than 

 feet, for they are used for "rowing" by free-swimming 

 copepods, but they can also be used to throw the 

 creatures into the air with a kind of kicking action, 

 resulting in multitudes of them falling to the surface 

 again like rain. 



Apart from the free-swimmers, which people the sea 

 in vast numbers defying computation, many forms are 

 parasitic, and these are usually larger than the free- 

 swimming kind. One of these larger forms is the Pennella, 

 a parasite on the whale, sometimes exceeding a foot 

 in length. Many of these parasitical copepods will 

 attack any host, but some specialize in fastening on to 

 one kind of animal. 



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