WHITEFISH OF THE LAKE OF GENEVA 



The waters of the sea also have their cycle of 

 nutrition, their progressive chain of devourers and 

 devoured. The stomach of a sardine, opened so that 

 we may find out what it has in it, shows us the remains 

 of microscopic vegetables and animals, mixed up with 

 fragments of floating creatures a little larger. In the 

 stomach of a herring, as in the whitefish of the lakes, 

 we usually find traces of those tiny crustaceans which, 

 themselves a part of the plankton, millions upon 

 millions of them, feed in their turn, upon microscopic 



Fig. 36. — Bosmina longispina, planktonic crustacean of the order 

 Cladocera. Length between \ and 1 millimetre. 



unicellular creatures. The cycle, beginning with the 

 latter, is continued by the little crustaceans and by the 

 creatures, as tiny as these last, which also feed upon more 

 minute beings. It continues again with the stronger 

 animals, not sardines or herrings alone but belonging 

 to other groups, molluscs and higher crustaceans. It 

 goes on to still larger animals, like the tunny, which 

 ruthlessly hunts down the anchovies, sardines, and 

 mackerel. It ends in the giants of the sea, huge 

 sharks, enormous whales like the cachalot. It is com- 

 pleted and complicated by the huge quantity and 

 diversity of the animals which live on the bottom, 

 settled there or practically so, which also take their 

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